Academic journal article Political Research Quarterly

Issue Politics in a Polarized Congress

Academic journal article Political Research Quarterly

Issue Politics in a Polarized Congress

Article excerpt


The standard explanation for increasing party polarization in Congress is based on factors that would affect all policy issues simultaneously. We show that this has not happened. We examine the dimensionality of legislative choice in the House of Representatives, scaling eighteen issues in each Congress from 1965 through 2004. We detect considerable variability in issue dimensionality, an evolution in the structure of choice over time, and changes in the relationship between party unity and issue dimensionality. Our findings suggest that polarization has occurred on an issue-by-issue basis, reinvigorating the debate over the role of policy substance in shaping congressional politics.


issues, dimensionality, party polarization, Congress

Polarization and partisanship in Congress have trended upward since the 1970s and conflict has increasingly become organized around ideological concerns (Poole and Rosenthal 1997; McCarty, Poole, and Rosenthal 2006; Lee 2009). These trends are typically viewed as institutionwide phenomena, intensifying across the years in both the House and Senate. Some scholars have pointed to aspects of the legislative process that are more or less resistant to these trends; for example, procedural votes are more likely to polarize the parties (Theriault 2008). For the most part, however, scholars have viewed the process of increasing polarization and the corresponding simplification of the choice space as consequences of societal developments (McCarty, Poole, and Rosenthal 2006), regional political realignments (Poole and Rosenthal 1997; Stonecash, Brewer, and Mariani 2003), or reforms to legislative rule and procedure (Rohde 1991; Theriault 2008).

These explanations are clearly credible, but they omit a very important component of congressional politics: the issues that generate voting coalitions. Some issues, like agriculture, tend to diffuse partisan polarization while others, such as macroeconomics, exacerbate it. Most if not all issues contain a left-right ideological component centering on government intervention in economic affairs. But as we show, many also contain crosscutting components that divide legislators by concerns that appear neither ideological nor partisan in nature.

The question is not whether Congress has become more polarized; this has obviously happened. Poole and Rosenthal (2001, Figure 1) document a strong and sustained decline during the postwar period in the improvement offered by the second dimension. The question is how this has occurred. In this article, we examine the evolution of issue dimensionality since the mid-1960s by scaling roll call votes within the Policy Agendas Project's topic categories. Our analysis indicates that the period of study was characterized by a series of issue evolutions in which individual issues became integrated into the partisan and ideological fabric of the political system.

We examine three aspects of issue dimensionality that together provide evidence that party polarization has proceeded on an issue-by-issue basis. First, we show that issues vary in their dimensionality. Some issues are readily captured by the unidimensional, ideological model of Congress while others are more complicated, requiring additional dimensions to explain members' voting behavior. Second, we identify an evolution in dimensionality over time, from multidimensional spaces toward unidimensional spaces. A simplifying choice space suggests that concerns orthogonal to ideology and party are becoming less central to the organization of congressional politics. Variation in the process of simplification-that is, different rates and different periods-suggests such changes cannot be the result of institution-wide phenomena that affect all issues similarly. Third, we demonstrate that party cohesion has something to do with these patterns, supplementing our study of issue-based dimensionality with an examination of issue-based party unity measures. …

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