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The Geographic Polarization of American Politics


This project addresses the question of whether American elections became more geographically polarized between 1972 and 2008. It finds that variation in partisan voting increased substantially over that time at both the state and regional levels. In particular, the Northeast and Pacific Coast became more strongly Democratic after the 1980s in both presidential and congressional elections, while the South and interior West remained solidly Republican.

I employ quantitative analysis of survey data to demonstrate that this trend can be largely explained by the increasing electoral salience of social and cultural issues, which divide Americans along regional lines to a greater extent than economic issues. The growing association of the national Republican Party with social conservatism has produced an electoral advantage in most of the South bolstered by an increasing edge over the opposition Democrats in aggregate party identification within "red" America. In more socially liberal regions of the United States, the Republican electoral position weakened substantially after the 1970s and 1980s, with Democratic identifiers becoming much less likely to defect to Republican presidential candidates in 1992 and thereafter.

I argue that these trends have significant consequences for American parties and the operation of Congress. Specifically, the growth of Democratic electoral strength outside the South has greatly reduced the number of moderate Republicans in both the Senate and House of Representatives, while centrists--elected mostly from the South and rural West--continue to constitute a sizable proportion of the congressional Democratic Party. This ideological asymmetry, though not often noted by previous studies of party polarization, suggests that the congressional parties do not operate as mirror images but instead maintain distinct strategic positions, with Republican congressional leaders able to command a higher degree of ideological unity among their members than their Democratic counterparts. The challenge faced by the Obama administration in pursuing an ambitious legislative agenda in 2009-2010, including reform of the American health care system, was a visible consequence of this distinction between the congressional parties: the presence of a large moderate bloc on the Democratic side complicated efforts to enact liberal initiatives despite large nominal Democratic majorities in Congress, while the lack of a significant number of moderate Republican officeholders largely frustrated the new president's attempts to gain bipartisan support for his proposals.

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