Elite-level Issue Dynamics: Assessing Perspectives on Issue Polarization

Transcription

1 Elite-level Issue Dynamics: Assessing Perspectives on Issue Polarization Daniel J. Lee Rachel A. Schutte Abstract We analyze elite-level issue dynamics of culture war issues in the U.S. since the 1970s to assess the extent to which they have transformed American party politics. Previous works on issue dynamics, which focus on changing levels in partisanship or polarization, at times confuse between three theories of issue change issue evolution, conflict extension, and ideological polarization. We argue that these theories differ on a second aspect of issue conflict: dimensionality that is, the relationship between political conflict on the issue in question and conflict on other issues. Our paper clarifies the similarities and differences across these perspectives. We analyze changes in the dimensionality of voting in the U.S. House on the environment, women s rights, gun control, abortion, and immigration to present a more comprehensive view of issue dynamics, while assessing the different perspectives of issue change. Our results suggest that these perspectives need further clarification and development, such as the consideration of degrees of an evolution. For many of these issues, issue conflict was simply absorbed by existing partisan cleavages, which is a testament to the durability of the American two-party system. Work in progress. Please do not cite without author permission. Assistant Professor of Political Science. Michigan State University. leedan@msu.edu Ph.D. Candidate. Department of Political Science. Michigan State University. rschutte@msu.edu

2 One of the most significant changes in American politics since the 1970s is the increased polarization of political elites. Poole and Rosenthal (2007) and Theriault (2008) analyze the divergence on a main liberal-conservative ideological dimension (see also Hetherington, 2009). Other researchers have looked within this broad ideological trend by studying polarization on individual issues, such as Civil Rights (Carmines and Stimson, 1989), women s rights (Wolbrecht, 2000, 2002), the environment (Lindaman and Haider-Markel, 2002), gun control (Lindaman and Haider-Markel, 2002), and abortion (Adams, 1997). Some observers describe the increased polarization on new issues as signaling the rise of a culture war, which stresses the increased salience of moral values, relative to traditional economic values (e.g., Hunter, 1991; Frank, 2004). In this paper, we clarify the nature of elite (members of Congress) polarization on specific issues in order to better understand issue dynamics. That is, we aim to develop a more comprehensive picture of how political conflict on polarizing issues changes over time. To accomplish this goal, we analyze how changes in issue polarization correspond with changes in the dimensionality of conflict on that issue. Previous works provide an incomplete picture of issue change because they only track changes in the degree of polarization or partisanship on the issue the difference in preferences (roll call voting) on an issue between the average Democrat and the average Republican. We argue that a measure of polarization only illustrates one aspect of issue change. Our paper places the polarization on a particular issue into perspective by observing how conflict on that issue changes in relation to conflict on other issues. Is issue change due to changes in the broader political environment or something peculiar about a specific policy area? And is polarization a sign of a culture war, or are these new issue conflicts simply a reflection of traditional partisan conflict? Our analysis of issue dynamics highlights the durability of American two-party system. The rise of culture war issues had the potential to disrupt the major parties, either by instigating sizeable shifts each party s coalition or by introducing an issue space for a successful third party. But as a casual observer of American politics knows, an increased importance of environmental issues, for instance, did not lead to the triumphant rise of the Green Party as a viable challenger to the two major parties. We instead show that many culture war issues have been absorbed by the existing party system, although there were some notable differences across issues. 1

3 1 Theories of issue change By focusing on changes in issue dimensionality, we highlight similarities and differences between various theoretical perspectives of issue change: issue evolution (Carmines and Stimson, 1989), ideological polarization (Poole and Rosenthal, 2007), and conflict extension (Layman and Carsey, 2002). 1 The purpose of this paper is both theoretical and empirical. We first clarify the theoretical connections, both similarities and differences, across these three perspectives of issue change. Our discussion in particular suggests the need for clarification on the empirical research regarding issue evolution. We analyze roll-call voting in the U.S. House on four issues that have been argued in the literature to be examples of an issue evolution: the environment (Shipan and Lowry, 2001; Lindaman and Haider-Markel, 2002), gun control (Lindaman and Haider-Markel, 2002), abortion (Adams, 1997), and women s rights (Wolbrecht, 2002). These works already demonstrate elite polarization on each of these issues. We extend their findings by observing how polarization tracks with changes in dimensionality, while also considering the more recently salient issue of immigration. Assessing changes in dimensionality to clarify and highlight the distinctions between these perspectives is important. For instance, the consequences of polarization according to issue evolution versus ideological polarization are quite different. What we call the strong version of issue evolution leads to a transformation of party conflict. Rather than reinforce the status quo, a cross-cutting issue rotates politics onto a new axis, such as racial politics during the Civil Rights era (the original example of an issue evolution, Carmines and Stimson 1986, 1989) or values/morality during the intensification of conflict over abortion policy during the 1990s. The polarization literature, on the contrary, claims that politics falls onto a structured liberal-conservative continuum with Democrats more liberal than Republicans, and more issues have become ideologically contentious over the past few decades. McCarty, Poole, and Rosenthal highlight the difference between these two perspectives in writing, For Carmines and Stimson [issue evolution], American politics has become the politics of race. We are suggesting that racial politics has become more like the rest of politics (McCarty, Poole and Rosenthal, 2006, 52). 2 1 Some of these works study elite polarization within a larger framework (e.g., Carmines and Stimson, 1989; Layman and Carsey, 2002). That is, they consider the consequences of elite polarization by analyzing the elite-mass linkage to assess issue change at the mass public level. Our paper is not concerned with this linkage. We are only interested in clarifying the nature of elite polarization e.g., the first step of an issue evolution. Since elites frame issue conflict for the mass public (Carmines and Stimson, 1989; Hetherington, 2001; Layman and Carsey, 2002; Levendusky, 2009), clarifying issue change at the elite-level is an important first step needed before one can turn to further analyzing the intricacies of the mass-elite linkage and issue change among the mass public. 2 To further see the significant difference, increased polarization on the existing cleavage likely decreases the likelihood of a strong evolution it is difficult for new issues to rise in salience when debate on current issues is so contentious. If partisan conflict is high and parties are starkly differentiated on some ideological dimension, then political elites would have difficulty raising a new cross-cutting issue to change the terms of debate, since there is already so much at stake under the status quo. 2

4 Our empirical analysis suggests that considering degrees of an issue evolution is beneficial. That is, rather than treat issue evolution as a yes or no concept, we find that some issues show more or less evidence consistent with an evolution. By appreciating the subtle differences across issues, we can order the issues in terms of the strength/significance of an evolution. We also reconcile contradictory accounts of issue conflict since the 1970s. Some observers stress the increased presence of a culture war, which has introduced newly divisive rhetoric into the political debate, challenging traditional, economic political arguments and old lines of division. Meanwhile, other researchers instead note the increasing partisanship and concurrent drop in the influence of cross-cutting cultural divisions (i.e., race issues) during that same time period. We show how both accounts are to some extent true. 1.1 Strong issue evolution Two versions of issue evolution have been asserted in the literature. The first, which we refer to as the strong version, is closely intertwined with the concept of realignment, as it makes specific claims on the nature of partisan change: the new issue is cross-cutting and changes the terms of political debate, altering the partisan cleavage (e.g., Carmines and Stimson, 1989; Carmines and Wagner, 2006). The second, which we refer to as the weak version, does not require any realigning element to the new issue and instead only focuses on the elite-public linkage: elites polarize on an issue, and the mass public follow elite cues to similarly polarize or sort. This less stringent view is what researchers currently often mean when alluding to the issue evolution perspective (see especially Stimson, 2004). In many published works, proponents of the issue evolution perspective make a very specific claim on the nature of partisan change. They (e.g., Carmines and Stimson, 1986, 1989; Carmines, 1991; Carmines and Wagner, 2006) assert that the issue instigates a realignment (although they also critique realignment theory, which we discuss further below). At the heart of the theory is the introduction of a cross-cutting issue that alters the existing partisan cleavage. Stressing the notion party realignment, Carmines and Stimson write: But occasionally issues rise from partisan obscurity and become so contentious, so partisan, and so long lasting that they come to define the party system in which they arise, to transform the grounds of debate which were their origin. This joint transformation of issues and party systems, which we call issue evolution, is realignment in the ordinary English usage of that term. [emphasis added] (Carmines and Stimson, 1986, 901) 3 3 Carmines and Stimson define realignment elsewhere as simply the transformation of an existing alignment caused by the intro- 3

5 Carmines states elsewhere that: [Issue evolutions] do not reinforce the existing party alignment. Instead, they cut across the direct line of evolutionary development. They emerge from the old environment, but once having emerged they introduce fundamental tensions into the party system and are inconsistent with the continued stability of old patterns. [emphasis added] (Carmines, 1991, 74) In an application of the issue evolution perspective, Adams writes: An issue evolution can produce the same result as a realignment, but the process unfolds over a longer period of time... Under the theory of issue evolution, a few rare issues exist with the capacity to instill fundamental and permanent changes in the party system. [emphasis added] (Adams, 1997, 719) Importantly, the issue must leave an indelible imprint on the party system (Carmines and Stimson, 1989, 13), whereby the new issue displaces (transforms) the previously dominant dimension of conflict. This perspective is consistent with the traditional view of partisan realignment (see Key, 1955; Sundquist, 1983; Aldrich, 1983; Miller and Schofield, 2003), and it has used a similar framework and language as the realignment literature. The introduction or a new issue, such as race, by strategic political elites can induce such a realignment, which can take several years and elections to occur. 4 Recent research on the rise of culture wars is also related to this stronger form of issue evolution. Especially since the 1980s and 1990s, so the argument goes, cultural, social and moral issues increasingly divide the public and politicians, rather than simply questions over the economy (for a review, see Fiorina, Abrams and Pope, 2005). Some researchers argue that traditional economic conflict has been in part replaced by a post-materialist dimension (Inglehart, 1981; Inglehart and Abramson, 1999). Previous research does not appropriately assess such changes to partisan cleavages and instead only base evidence on comparisons of voting scores (e.g., party unity) on a particular issue over time. Increased intra-party consistency and inter-party difference are taken as evidence of the first step of an issue evolution (the second step being mass public response). Showing an increase in partisan differences on an issue, however, falls short of conclusively showing a strong issue evolution. That is, one cannot observe, for example, whether an evolution has occurred on abortion by simply observing votes on abortion. One duction of a new dimension of conflict (Carmines, 1994, 77; Carmines and Wagner, 2006, 69). 4 The difference between issue evolution and traditional realignment theory that proponents have noted is that the former is a gradual process, while the latter often posits sharp change from a critical election (e.g., Key, 1955; Burnham, 1970). 4

6 needs to also assess how voting on abortion changes in relation to voting on other issues, in particular issues related to the party cleavage that dominated before the conjectured evolution. To be clear and fair, even the strong issue evolution perspective does not necessarily call for a complete displacement of the originally dominant dimension. Carmines and Stimson (1989) give considerable thought to the similarities between issue evolution and realignment (see also Carmines and Wagner, 2006), and they note that issue evolution is a considerably more subtle phenomenon compared to the realignments during the Civil War and the New Deal (Carmines and Stimson, 1989, 20). Our theoretical discussion and empirical analysis suggests that this perspective may benefit from a more clear and explicit description of the characteristics of this subtle phenomenon (with a more precise description of how it differs from realignment). Our clarification and empirical analysis aids in determining degrees of an issue evolution. 1.2 Weak issue evolution The second version of issue evolution, which we refer to as the weak version, does not require the new issue to realign political conflict (i.e., displace or alter the old partisan cleavage). 5 This view is what some researchers now mean when thinking of the issue evolution perspective, which Stimson (2004) and numerous applications (e.g., Adams, 1997; Wolbrecht, 2000) of issue evolution adhere to albeit at times inconsistently, which we point out below. We find only one instance (to our knowledge) of the issue evolution perspective explicitly theorizing a weaker version of issue change. Stimson writes in his updated discussion of the topic: We know that a two-party system tends to create a single issue division that is stable over time, that it generates new issues as a predictable response to the needs of otherwise losing parties to shake up the system, and that these new issues gradually become incorporated into the old issue configuration with the passage of time. [emphasis added] (Stimson, 2004, 69) This formulation is somewhat different from earlier work by de-emphasizing the realigning nature of evolutions and it is telling that Stimson characterizes issue evolution as issue alignment, rather than realignment, in this more recent book. Although applications of the issue evolution perspective show evidence in support of the weak version, they still have tended to use the language of the strong version. One can see this in the Adams (1997) 5 We do not mean to use the term weak in any negative sense. We use the terms strong and weak to only point out that the strong version adds the requirement on changes in dimensionality (realignment) that imply a more significant change to partisan conflict from an evolution. The weak version does not require any such change to the party system and instead argues that new issues, although originally cross-cutting, will align onto pre-existing partisan cleavages as the issue evolves. 5

7 quote above. Wolbrecht (2000) also conflates the two versions in her analysis of women s rights. Wolbrecht (2000, 4) in parts supports the strong version, at one point contending, polarization over women s rights has emerged as one of the most readily identifiable, if not defining, distinctions between the parties (emphasis added). The theoretical discussion also draws heavily from the classical realignment literature, and views issue evolution as directly extending that literature (Wolbrecht, 2000, ). At the same time, Wolbrecht alludes to the weak version in her theoretical discussion, which is based on the one-dimensional Downsian model (Wolbrecht, 2000, ), since any discussion of realignment (strong version) should utilize a multi-dimensional model. This one-dimensional focus then contributes to her empirical approach in supporting the weak version in arguing that elites instigated an evolution when [w]omen s rights issues took on a sharp dimensionality, mapping onto the left-right political spectrum (Wolbrecht, 2000, 12). Such mixing and matching of the strong and weak versions, we argue, is problematic, since it masks potentially distinct issue dynamics. The difference between the strong and weak versions puts into perspective the significance of partisan changes on individual issues. Quoted above, Wolbrecht claims that women s rights is now perhaps the defining distinction between the parties. The problem with this statement is that if the weak version is correct, then one could pick nearly any issue today and claim that it is a defining distinction between the parties, since the parties are highly polarized on nearly all issues. One would have difficulty in judging whether women s rights, the environment, abortion, immigration, tax policy, social security, or gun control is better or worse at distinguishing between the parties. The confusion between the weak and strong versions is in the usage of the term realignment. The strong version, in alluding to comparisons between issue evolution and classical realignment theory, asserts that party change is a true realignment, in the sense of changing dimensions of political conflict (e.g., Burnham, 1970; Sundquist, 1983; Aldrich, 1983). The weak version instead talks about realignment on the issue in question. That is, there is no assertion of how change on that issue changes its relationship to conflict on other issues. It simply posits a re-sorting of parties on that issue. 6 6 To clarify the unique quality of true realignment, suppose we have a liberal to conservative ordering of legislators on the preexisting dominant dimension. Now suppose we have a new issue, such as abortion, that comes onto the scene and is initially crosscutting. If issue positions change such that preferences on abortion match preferences on the pre-existing dominant dimension, then a strong issue evolution did not occur, even if policy preferences on abortion polarized. The abortion issue, as it became increasingly structured, did not leave an indelible imprint on the party system preferences (ordering of legislators) on the pre-existing dominant dimension did not change. Instead, party positions on abortion realigned to fit onto the dominant ideological dimension. This difference between realignment instigated by a new issue versus realignment on an issue is critical. 6

8 1.3 Ideological polarization The third perspective is that supposed issue evolutions were simply instances of increased issue ideological consistency (partisan sorting) and a reflection of a general trend of polarization on the pre-existing dominant ideological dimension since the 1970s. Poole and Rosenthal (2007) and McCarty, Poole and Rosenthal (2006) take this view, which we refer to as ideological polarization. When a new issue emerges, conflict is not necessarily partisan. It may be unstructured and cut across partisan lines. As the issue develops, the parties incorporate it into the existing major party cleavage Democrats take one side and the Republicans take the other side. That is, the the competing sides on the issue sorts into the two party s camps. The parties polarize on these issues because the parties are polarized in general (and increasingly so since the 1970s) and not uniquely on the issue in question. McCarty, Poole and Rosenthal (2006) and Poole and Rosenthal (2007) critique the issue evolution perspective by arguing that conflict on racial issues now simply reflects economic conflict, which is the canonical ideological dimension. 7 Looking at studies that consider the consequences of elite polarization, we see similarities to the issue evolution literature. Hetherington (2001) and Levendusky (2009) consider at the implications of elite ideological polarization, arguing that voters have become more sorted, whereby voters holding liberal (conservative) issue stances are more likely to associate themselves with the Democratic (Republican) party. The increase in sorting is due in large part to polarization among political elites, which clarifies the party s reputations on those issues. The elite mass-linkage, which is also a part of the conflict extension perspective (discussed in a following section), is quite similar to the issue evolution perspective. 8 To illustrate this point, Figure 1 maps the processes of voter sorting and issue evolution, which are taken directly from Levendusky (2009, 13) and Carmines and Stimson (1989, 160). Notice that the sorting process described by Levendusky appears to be identical to the issue evolution perspective. So on the one hand, issue evolution and partisan sorting are essentially the same by stressing how polarization among elites clarifies issue differences, which is then reflected by changes in the public. On the other hand, there is a significant difference between strong issue evolution (Figure 1.B, Carmines and Stimson, 1989) and the other perspectives on party issue dynamics (Figure 1.A, Levendusky, 2009). 9 The difference is that in a strong issue evolution, the polarizing issue is some new cross-cutting issue that alters the partisan cleavage 7 See also Abramowitz (1994), who questions the evidence of Carmines and Stimson (1986, 1989) on similar grounds of ignoring the relationship of conflict on racial issues with conflict on other issues. 8 There are to be sure differences in the specific dynamics of the elite-mass connection, but since our focus is on elite-level changes, we ignore those differences. 9 Levendusky (2009) appears to stress the consequences of general trends of elite polarization and does not give much attention to issue-specific differences. He also gives no mention of a cross-cutting quality of changing issues and instead focuses on increased ideological consistency across the issues. 7

9 an added condition not explicitly stated but yet differentiates the two theories in Figure 1.A and 1.B. [Figure 1 about here.] 1.4 Conflict extension The fourth perspective on issue dynamics is conflict extension (Layman and Carsey, 2002; Layman et al., 2010). Although the unidimensional argument of ideological polarization of Poole and Rosenthal (2007) differs from the multidimensional conflict extension perspective, we take that difference to be somewhat semantic. In both perspectives, issue displacement is not necessary for polarization on a new issue and in this way differs from issue evolution and other realignment perspectives (e.g., Burnham, 1970; Sundquist, 1983; Aldrich, 1983; Carmines and Stimson, 1989). Furthermore, although conflict extension is multidimensional, the parties positions across issues are strongly correlated. That is, if a party takes a conservative stance on one issue, then they are conservative on another. This correlation essentially reduces the multidimensional space into a single liberal-conservative dimension that describes conflict across all issues. Because we see a larger substantive difference between the ideological polarization and issue evolution perspectives, we give most attention to that comparison. 1.5 Simplifying to two general perspectives Our intention is not to simplify each perspective to minimize their unique contributions. But when focusing on the dynamics of issue change at the elite-level, there are two primary aspects of change on which we make comparisons. One is the increased partisan division and polarization on issues. The second is how changes on the issue in question influences how conflict on that issue compares to conflict on other issues. All four perspectives agree that elite polarization is evidence of issue change. The difference then lies in the claims made on the significance of the new issue does the new issue add something new to party conflict, or does it merely reinforce pre-existing conflict? The odd perspective out in this regard is strong issue evolution, which posits a realigning quality of new issues. The other three perspectives (weak issue evolution, conflict extension, ideological polarization) posit that as a new issue evolves, it works its way into the pre-existing dimension of conflict. 8

10 2 Assessing party change and issue polarization Our empirical approach is to observe changes in the dimensionality of roll call voting in the U.S. House on an issue. Different patterns will be consistent with different perspectives on issue polarization. (See Appendix A for a spatial representation of the following discussion.) Discussing our expectations in terms of the data that we use helps clarify our main points. Our analysis utilizes Poole and Rosenthal s firstand second-dimension NOMINATE scores, which have the commonly accepted interpretation that the first dimension captures government intervention in the economy and the second tends to capture regional conflict, which during most of the recent era is understood to be civil rights (Poole and Rosenthal, 2007). Each dimension score runs from 1 to 1 (liberal to conservative), and we interpret vote models that use a member s NOMINATE score to predict her roll call vote and interpret the results in the following way: First-dimensional: If voting on an issue is explained by existing partisan cleavages, then first-dimension NOMINATE scores largely predict voting behavior on that issue. Cross-cutting cutting: Second-dimension NOMINATE scores will significantly predict voting on that issue. Mixed: If the issue is somewhat cross-cutting, then scores on both dimensions are needed to predict voting on that issue. 10 Although Poole and Rosenthal (2007) have shown that overall roll call voting has become more onedimensional since the 1970s, our analysis examines differences across issues within that larger trend. If there is a strong issue evolution, then legislator preferences on some other dimension adds independent information to preferences on the pre-existing dominant partisan dimension of conflict (first dimension NOMINATE). In other words, if the environment (or abortion or women s rights) is transformative, then conflict on that issue should not simply reproduce pre-existing partisan conflicts. It should bring to the table something unique and new, moving beyond the first dimension NOMINATE (i.e., the cross-cutting or mixed cases). To further illustrate what empirical patterns are consistent with each perspective on issue polarization, Figure 2 depicts three potential patterns of correlation between legislators preferences on a specific 10 Some caveats apply. Is that it is possible for a cross-cutting issue not to map onto the second dimension NOMINATE, which captures an issue dimension for issues that have many roll calls that similarly influence voting decisions of many members. Since the issues that we are analyzing make up a small proportion of votes, this concern may be pertinent. Low predictability of voting based on either dimension of NOMINATE scores (voting does not fit into the dimensions recovered by the NOMINATE procedure) can also describe an issue that is cross-cutting. For space considerations, leave the analysis that considers this possibility in Appendix C. Additionally, low classification rates using scores from either dimension is also consistent with the possibility of a mixed issue. 9

11 issue, like the environment (say a scale of 1 pro-environment, to 1 anti-environment), and first and second dimension NOMINATE scores ( 1 liberal, to 1 conservative) over time. In all three hypothetical scenarios, we start the time series at a point where voting on the environment is not entirely structured along a single ideological dimension (although we suppose in our example that it is slightly more structured on the first dimension) voting on the new issue is not yet structured. From time 0 to time t, we move through an adjustment phase, where the parties are beginning to change voting patterns on the environment as an attempt by strategic elites to instigate an evolution. After time t, the three hypothetical situations differ. [Figure 2 about here.] Figures 2.A and 2.B are illustrations of potential strong issue evolutions. Figure 2.A depicts the case where the issue (environment) becomes fully structured along the second dimension. In this case, voting is entirely independent (orthogonal) to the pre-existing partisan cleavage the cross-cutting case. In Figure 2.B, preferences and voting on the environment are increasingly explained by the second dimension. But in the end it remains a product of preferences on both ideological dimensions the mixed case. 11 This case is where a strong evolution results in only a partial displacement. 12 Figure 2.C depicts the case where conflict on the environment is subsumed into the dominant ideological dimension, which is consistent with the perspectives of weak issue evolution, conflict extension, and ideological polarization. 13 After the adjustment period, preferences on the environment are increasingly correlated with preferences measured by the first dimension of NOMINATE. 3 Analysis We analyze changes in the dimensionality of roll call voting on the environment, gun control, abortion, women s rights, and immigration. We also consider immigration as a more recent issue that some view as part of the contemporary culture war in American politics. Voting on tax and budget is used as a baseline for comparison canonical economic issues that are broadly understood to be measured by first-dimension NOMINATE. Our analysis shows that voting on all issues is increasingly predictable by 11 See Figure 8 in Appendix A for an alternative graphical representation of these same scenarios. 12 A slightly amended version of Figure 2.B also depicts a possible strong issue evolution. Suppose that the dotted line (correlation between preferences on the environment and second dimension NOMINATE) does not increase (remains flat). Even if voting on the issue is not increasingly structured on the second dimension NOMINATE, that issue is moving beyond the first dimension (correlation with first dimension NOMINATE decreases). As stated above, for issues that make up a small portion of votes, it may be structured on a dimension not captured by the NOMINATE scaling procedure. This point is covered further in Appendix C. 13 This again assumes that the content of first dimension NOMINATE does not change over the observed time period. This assumption is supported by McCarty, Poole and Rosenthal (2006) and Poole and Rosenthal (2007), as well as our use of budget and taxation votes as a baseline. 10

12 first-dimension NOMINATE scores over time, although the timing for each issue differs. This pattern is shown first using aggregate-level data on the environment, then by using a vote-level analysis for all of the issues. Our results call into question previous claims of realigning evolutions on many of these issues. 3.1 Data Our data set of roll call voting in the U.S. House spans the 92nd to 110th Congresses (1971 to 2008), which is the time frame of the supposed issue evolutions. 14 By analyzing roll call votes, we are of course limiting ourselves to observed conflict on issues that successfully make it onto the legislative agenda. Observing these votes (a byproduct of whatever agenda-setting powers the parties may have) is not problematic for our purposes. In fact, observing the votes that do make it to the House floor is precisely what we should analyze to assess issue change, since part of an evolution or change on an issue can relate to agenda control. 15 To measure House member placement in a two-dimensional policy space, we use first- and second-dimension NOMINATE scores. Data availability allows for a more in-depth analysis of voting on the environment. 16 We utilize scores from the League of Conservation Voters (LCV) to measure legislator preferences on the environment, which vary from 0 to The score is calculated as the percentage of votes, which are deemed important to the LCV, that the member voted for the group s side. Higher scores denote a higher support for pro-environment (liberal) positions. Because our analysis does not require intertemporal comparisons of LCV scores, we simply use the raw scores rather than adjusted scores (Shipan and Lowry, 2001). These measures are assumed to capture preferences on a particular dimension, which influences roll call voting behavior. LCV scores capture preferences on environmental issues, and NOMINATE scores capture preferences on the first and second ideological dimensions. As earlier discussed, implicit in our analysis is the assumption that there was not a significant shift in the content of the first-dimension NOM- INATE during this time period, which has been substantiated in earlier work (e.g., McCarty, Poole and 14 Note that electronic voting was instituted in the 93rd Congress. 15 The desire to keep party-splitting issues off of the legislative agenda suggests that our results might underestimate the extent to which issues are cross-cutting (and hence evolutions).but we believe agenda control is one tool that the parties (especially majority) can use to shape issue conflict. That is, whether the parties take opposing views on an issue is in part a product of their strategic choices how salient will the parties make an issue and will it make it onto the (legislative or campaign) agenda? For instance, for the canonical example of issue evolution (racial politics in the 1950s and 1960s), the strategic choice of pushing civil rights onto the agenda was a major contributor to change on that issue (Carmines and Stimson, 1989). This justifies the use of roll call voting behavior to analyzing issue dynamics in all previous work on issue change, as well as our own presented analysis. Also see some discussion of agenda control in Appendix C. 16 The other issue areas of abortion and women s rights lack available interest group scores. The National Right to Life Committee (NRLC) publish scorecards for members of Congress, but this is only available since the 105th Congress. 17 Unlike for some other interest group scores, such as the Americans for Democratic Action (ADA) scores, the number of votes included in the LCV score varies Congress to Congress. The number is roughly between 20 and 40 votes per Congress. 11

13 Rosenthal, 2006), as well as in our later analysis of the taxation and budget baseline. Lastly, our vote-level analysis requires a determination of which roll-call votes deal with each policy area. We use the Public Institutions and Public Choice (PIPC) House Roll Call Database to make these determinations First look: The Environment Our first brush at analyzing issue change focuses on the environment, which utilizes the LCV scores. Our first piece of evidence is to observe correlations between legislators LCV scores and their first- and seconddimension NOMINATE scores by Congress. The potential patterns were discussed earlier and depicted in Figure 2. In this portion of the analysis, we flip the NOMINATE scale (multiply by 1) so that the LCV and NOMINATE scales both run from most conservative to most liberal. [Figure 3 about here.] The patterns observed in Figure 3 are striking and consistent with the claim that the environmental issue dimension has collapsed onto the dominant ideological dimension since the 1970s, which most resembles Figure 2.C. The correlation between LCV and first dimension NOMINATE scores increases over the time series from under 0.6 to above 0.9. Conversely, the correlation between LCV and second dimension NOMINATE scores drops from just under 0.6 to less than 0.1 over the same time period. This increase in first-dimensionality coincides precisely with the increase in elite polarization on the environment (Shipan and Lowry, 2001; Lindaman and Haider-Markel, 2002) and is consistent with the weak version of issue evolution. Rather than introduce a new partisan cleavage, voting on the environment polarized as it was subsumed into the main dimension of partisan conflict. Karol (2009) runs a similar analysis for abortion and gun control. Rather than use interest group scores, he creates issue support scores (based on roll call votes), which shows the same general pattern of correlations. Those issues, like the environment, appear to have been absorbed by first-dimension NOMINATE over time. 19 Looking at aggregate voting data and correlations only gives a broad overview of issue change. We can provide more nuance in illustrating how an issue has collapsed onto the main ideological dimension by using a vote-level analysis. The basic approach is to estimate various probit models that predict votes on a 18 Data are available at 19 We choose to limit portions of our analysis to the environment by using LCV scores, since the other issues have a smaller and more variable number of roll call votes per Congress (with some Congresses having zero votes). Scores for the other issues are likely less accurate measures of preferences, given the small number of votes from which they are based on. 12

14 given issue within a Congress. The models differ in the independent variables included, and the predictive success of each model is compared to gauge which factors (dimensions) most influence voting. 20 The dependent variable is the vote, coded 1 if yea and 0 if nay. The independent variables included are either just first-dimension NOMINATE, both first- and second-dimension NOMINATE, and for our analysis on the environment the LCV score. To assess model fit, we compare the percent classified correctly i.e., the percentage of votes that are correctly predicted by the model. 21 That is, for each issue, we sum the total number of correctly predicted votes and divide by the total number of votes cast. This provides us for each issue in a given Congress the proportion of correctly classified votes. 22 This analysis allows us to determine what factors (dimensions) contribute most to voting on an issue. As an example, suppose we are interested in comparing a model that uses first-dimension NOMINATE scores to a model that uses LCV scores to predict votes on the environment. For each environmental roll call vote, we estimate the equations, p i = α 0 + α 1 1 st -d NOMINATE i + ε (1) p i = β 0 + β 1 LCV i + ε (2) where (1) is the one-dimensional NOMINATE model and (2) is the LCV model, p i is the probability legislator i votes yea, and ε is a normally distributed error term. Using the estimated parameters, we then predict whether a legislator votes for or against the measure, and a vote is correctly classified if the legislator votes how the model predicts. We do this for every environmental roll call vote during a Congress and then aggregate, calculating the percentage of environmental votes correctly classified in that Congress. If firstdimension NOMINATE captures conflict over the environment, then we would expect classification rates from the first NOMINATE model (1) to be equal to classification rates for the LCV model (2). If environment is not captured by the first ideological dimension, then the LCV model will produce higher classification rates. 20 Another possible measure of issue dimensionality is the angle of the cutting line for each roll call vote. See the Appendix for a more in-depth discussion of cutting lines. In the two-dimensional NOMINATE space, a vote that is first-dimensional will have a cutting line perpendicular to the x-axis (90 degrees). The more important the second dimension, the greater the deviation the cutting angle will be from that 90 degree line (either towards 0 or 180 degrees). However, given the caveat that the cross-cutting nature of the issues we are considering might not be captured by the second-dimension NOMINATE scores, cutting angles suffer from ignoring that possibility. For that reason, we use vote classification. 21 An alternative measure of model fit is the proportional reduction in error (PRE) (Poole and Rosenthal, 2007; McCarty, Poole and Rosenthal, 2006). The PRE avoids inflation of classification success from unanimous votes. Since we are interested in within-vote comparisons, rather than over time comparisons, this concern is not problematic for our results. We use vote classification because it is a straightforward and intuitive measure. 22 We exclude all unanimous votes from our analysis. 13

15 We can also measure the extent to which the issue is structured off of the first dimension by comparing classification success of the two models, p i = α 0 + α 1 1 st -d NOMINATE i + ε (3) p i = β 0 + β 1 1 st -d NOMINATE i + β 2 2 nd -d NOMINATE i + ε (4) If the issue is highly structured on the first-dimension, then (4) will not improve classification success over (3). On the other hand, if the issue is structured off of the first dimension, then (4) will improve classification success. 23 A few patterns emerge in Figure 4. First, the classification rate trends upward for all models. Second and more relevant to our analysis, comparing the two models that include NOMINATE scores, accounting for a second dimension adds less over time to predicting votes (the gap in the percent correctly classified decreases over the time span). In the 93rd Congress, including second dimension scores increases the percent classified by around 2.7 percentage points. By the 110th Congress, the second dimension improves the model prediction by less than one percentage point. These two observations reflect the general trend in roll call voting over this time period (Poole and Rosenthal, 2007). And importantly, this general trend applies specifically to votes on the environment. Contrary to the strong version of issue evolution, the conflict on the environment is increasingly coalescing on the first dimension. A last observation is that the model that only includes the LCV score most clearly outperforms the 1st-dimension NOMINATE model only during a few of the early Congresses (93rd through 95th), which is the the period where preferences on the environment is least correlated with the 1st-dimension NOMINATE and most correlated with the 2nd-dimension scores (see Figure 3). That is, preferences on the environment are increasingly reflecting preferences on the 1st dimension, shown by the similar classification rates based on predictions using 1stdimension NOMINATE scores versus LCV scores. [Figure 4 about here.] A few conclusions can be drawn from this analysis. First, voting on the environment indeed fits a spatial model of voting. Models that use NOMINATE scores to predict votes perform essentially as well as using a more specific measure of environmental support (LCV score). Second and most central to our discussion, the environment has collapsed nearly entirely onto the main liberal-conservative ideological 23 A caveat (also stated in an earlier footnote) is that a preferences on a cross-cutting issue may not be captured by second dimension NOMINATE scores classification rates may be small regardless of what scores are used. We also account for this possibility in Appendix C. 14

16 dimension by the 110th Congress, which is not consistent with a strong evolution. The improvement of fit in that Congress of the two-dimensional over the one-dimensional model (just under one percentage point) is slightly below the improvement when looking at all non-unanimous votes (Poole and Rosenthal, 2007). The pattern of increased one-dimensionality from the 93rd Congress based on Figures 3 and 4 is striking, and it corresponds with increased polarization on that issue (Shipan and Lowry, 2001; Lindaman and Haider- Markel, 2002). That is, voting on the environment polarized as roll call voting on that issue increasingly reflected voting patterns on traditionally ideological and partisan issues (first dimension NOMINATE), which was polarizing during that time independent of any changes in environmental politics (McCarty, Poole and Rosenthal, 2006; Theriault, 2008). 3.3 Environment, Abortion, Gun Control, Women s Rights, and Immigration Previous work on issue change and issue evolution has focused on the increased partisanship in roll call voting. Figure 5 plots for each issue area the percentage of roll call votes that are party votes (defined in this figure as votes that two-thirds of Democrats vote in opposition to two-thirds of Republicans) in each Congress for each issue. We use a slightly higher threshold (than, say, 50-50) to track more intense partisan differences. The reader should take some of these patterns with a grain of salt, since some issues had only only one roll call vote in a Congress e.g., immigration in the 96th Congress (see Appendix B for the number of roll calls per Congress for each issue). This figure largely corroborates earlier research, which use varying issue codings. Generally speaking, voting has become increasingly partisan, especially since the early 1980s. [Figure 5 about here.] To simply conclude that politics on these issues have become more partisan glosses over potentially important differences across the issues and does not help adjudicate between the various theories of issue change. To dig deeper into the issue dynamics to assess any differences across issue areas, we run the vote classification analysis for each issue, which utilizes first- and second-dimension NOMINATE scores as the predictors of roll call voting i.e., we estimate equations (3) and (4). Figure 6 presents our results for all four issues of purported evolutions, as well as immigration. To further highlight potential differences between these new issues and traditionally ideological and partisan issues, we present results on economic/tax/budget votes as a baseline. [Figure 6 about here.] 15

17 A couple general observations are immediately evident. Voting for all issue areas has become increasingly predictable over the time period (upward trends in Figure 5.A). Even for economic issues, classification success is lower for earlier Congresses (around 83% in the 92nd Congress), but that reflects a general pattern of low vote predictability during that time, which has given way to higher predictability in recent Congresses (McCarty, Poole and Rosenthal, 2006). A second observation is that all issue areas have become increasingly one-dimensional (downward trend in Figure 5.B). As expected, economic policy is consistently close to a first-dimensional issue controlling for the second dimension does not add much to vote prediction, and there is little Congress-to-Congress volatility compared to the other issues. But even for that issue, the second-dimension did contribute somewhat to voting during the earlier years. One can remember, for instance, the support by some Democrats for Reagan s spending and tax cuts during the 97th Congress ( ). All in all, the pattern for economic votes provides a basic baseline on which to compare the other issues. Although there is quite a bit of variability across issues (which we delve into further below), the general pattern is that the percent improvement from the two-dimensional model at times hovers above the line for economic policy during the earlier periods in Figure 5.B., but they have by the last Congress in our data set (110th Congress) converged. That is, over time, roll call voting for all the issues in our analysis have increasingly reflected conflict over traditional economic issues, and by the 110th Congress all issues are similarly one-dimensional (percent improvement is roughly 1.5% for all issues). We assess changes in the percent improvement of the two-dimensional model, covering each issue in turn in order to point out differences across the issues. 24 In Appendix C, we assess changes in overall model fit to account for the possibility that cross-cutting issues are are not necessarily captured by seconddimension NOMINATE. Due to space considerations, we leave that discussion for an appendix because of the striking patterns we observe for the percent improvement from the two-dimensional model Environment and women s rights During the early Congresses, there is some evidence that the environment and women s rights were indeed emerging as a structured cross-cutting issue. The gap between the percent classified for the oneand two-dimensional models is consistently largest for environmental issues during the earlier Congresses (up through say the 96th Congress). Consistent with earlier accounts of the women s rights movement, 24 One may of course like to have clear cut statistical significance tests when making such comparisons of model fit. Unfortunately, none is available, but we believe that much can still be gathered from our analysis. Herron (1999) does provides a method to estimate standard errors for classification rates of individual roll calls, based on the uncertainty in each member s votes. We, however, are aggregating roll calls within a Congress, and we are not aware of a method to recover standard errors in such a case. We are also not aware of a likelihood ratio test that can pool across all vote models within a Congress. 16

18 conflict on that issue was cross-cutting soon after passage of the Equal Rights Amendment by the House and Senate in the 92nd Congress. Figure 5 suggests that this did not really occur until the 94th Congress ( ), where the percent improvement of the two-dimensional model reaches a high point. Since that period, however, as for the environment, the issue immediately began to fall back onto the existing partisan cleavage as voting polarized, rather than redefine partisan politics Abortion Since these are indeed distinct issues that have different histories, it is not surprising that the timing of their rise and falls appear to be different. Out of the five issues that are in our analysis, abortion and gun control show the most stark differences. 26 Voting on abortion during the period soon after Roe v. Wade is characterized by low predictability, regardless of whether one accounts for a second dimension (see Appendix C for more discussion on this point). Evidence of abortion as a structured cross-cutting issue does not begin to emerge until the very end of the 1980s and the early 1990s. Its pinnacle coincides with the Republican Revolution from the 1994 congressional elections controlling for a second dimension increases classification success by over eight percent in the 104th Congress. Immediately following the 104th Congress, however, abortion began to incorporate back into the first dimension, and looking at voting in the 110th Congress, we see that abortion has been fully absorbed into the first dimension. What is especially interesting about abortion is that the era during which abortion is systematically a cross-cutting issue is precisely a period of a sharp increase in polarization (the 1990s). Women s rights and the environment, however, show a trend of decreased contribution of second-dimension NOMINATE scores during that time. Thus, the interesting change for abortion is not simply that roll call voting became more partisan. Rather, something beyond partisanship systematically influenced the votes for some members, even while partisanship was intensifying. 25 Notice that the rise of environmental issues is not captured during the time period of our analysis. For abortion and women s rights, we observe the full dynamic : (1) the issue is structured, if at all, on the first dimension, followed by (2) a period of change from a potential evolution (second dimension increasingly influences voting), followed by (3) the issue collapsing back onto the first dimension. Our data on the environment appears to catch the dynamic in period 2 (in Figure 3, at time t ). It turns out that voting on the environment leading up to the 92nd Congress was not as consistently a first dimensional issue as for the other three issues when moving into their transitional phases. For instance in the 83rd, 85th, and 87th Congresses, the percent improvement of the two-dimensional over the one-dimensional model were 5.2, 3.3, and 0.8 percent, respectively. But regardless of the structure of voting on the environment leading into the 1970s, the pattern after that point is clear: it has increasingly become a first-dimensional issue. 26 Adams (1997) and Wolbrecht (2002) do not suggest, however, any significant differences in the timing of the evolutions. Both argue that the issue evolutions began in the 1970s. We do not find this to be the case. 17

19 3.3.3 Gun Control As for abortion, gun control roll call votes show evidence of systematic influence of the second dimension. After gun control made a sustained presence of the legislative agenda by the 99th Congress, voting increasingly was structured on the second dimension, reaching a high-point in the 104th Congress. Furthermore, both votes in that Congress were party votes. Thus, as for abortion, even though voting was highly partisan, some additional factor (dimension) systematically influenced votes. But in the end, gun control fell back onto the first dimension by the 110th Congress, matching the same pattern as for abortion Immigration Immigration shows quite a bit of variability in the earlier Congresses, in part due to the small number of roll call votes per Congress. But over time, variability decreases and the issue has become increasingly one-dimensional. Notice that there is a small interruption in that trend, however, during the 108th and 109th Congresses. That bump in the dimensionality of voting coincides with heightened discussion of immigration reform, which crescendoed with mass protests across the country in For the most part, the issue was highly partisan with battle lines largely drawn between the Democratic and Republican parties. Further analysis, however, shows that party was not the only determining factor of roll call voting. 3.4 A culture war? Graphical examples We analyze three roll call votes on abortion, gun control, and immigration to help clarify how an issue can be both highly partisan and influenced by some additional (non-partisan, second) dimension. Doing so also shows how the small bump for immigration in the 108th and 109th Congresses compares to the larger and more sustained periods of second-dimension vote classification improvement for abortion and gun control. Immigration bill in the 109th Congress: Border Protection, Anti-terrorism, and Illegal Immigration Control Act of 2005 (H.R. 4437). Yea vote is for more restrictive immigration policy. Abortion bill in the 104th Congress: Partial-Birth Abortion Ban Act of 1995 (H.R. 1833). Yea vote is for more restrictive abortion policy. Gun control bill in the 104th Congress: Gun Crime Enforcement and Second Amendment Restoration Act of 1996 (H.R.125). Yea vote is for less restrictive gun control policy. Figure 7 plots each House member s NOMINATE score in the two-dimensional space (that is, using both the first- and second-dimension scores). We distinguish between three groups: (a) those who were 18

20 incorrectly classified by the one-dimensional model but correctly classified by the two-dimensional model, (b) the remainder who voted yea, (c) the remainder who voted nay. [Figure 7 about here.] First note that members in the left cloud of NOMINATE scores are Democrats and members in the right cloud are Republicans, which depicts the well-documented polarized contemporary Congress (e.g., Theriault, 2008). For all three roll call votes, the one-dimensional model (roughly) predicts that Democrats (left cloud) vote nay and Republican (right cloud) vote yea. There are some members from both parties that are misclassified (squares in the left cloud, dots in the right cloud). Important for our purposes, we can see a distinct pattern of which members are correctly classified once we account for second-dimension NOMINATE scores (the X s) i.e., which members votes are corrected by the two-dimensional model. For all three votes, notice that there is a cluster of Democrats on the high end of the 2nd-dimension who are correctly classified in the two-dimensional model, as well as a (smaller) cluster of Republicans on the low end who are correctly classified once second-dimension scores are included as a predictor. These are Democrats who are predicted to vote yea once we account for their second dimension score (25 Democrats for the abortion vote, 37 for gun control, 18 for immigration). For the Republicans, these are members who are correctly predicted to vote nay once we account for the second dimension (4 Republicans for the abortion bill, 26 for gun control, and 1 for immigration). These figures help visualize the differences between a strongly versus weakly two-dimensional issue. More members votes are corrected by the two-dimensional model for the abortion and gun control votes compared to the immigration vote. These figures also suggest that second-dimension NOMINATE systematically captures some elements of a culture war. We can interpret the y-axis as capturing social/moral conservatism with higher values as more conservative. In these examples, members who are high on the y-axis are more likely to vote for more restrictive immigration and abortion policies and less restrictive gun control. Thus, the claim that moral attitudes influenced roll call voting systematically is somewhat true it is captured (to some degree) by second-dimension NOMINATE. The culture war, however, did not displace traditional politics. Rather we see that it influences (independent of partisanship/first-dimension) only a handful of members, and the number varies across time and issues. 19