In This Article Expand or collapse the "in this article" section Partisan Polarization in the US Congress

  • Introduction
  • Review Articles
  • Historical Roots
  • An Unpolarized Congress
  • Measuring
  • Asymmetric Polarization
  • Institutional Causes
  • Relationship to Unorthodox Lawmaking
  • Partisan Warfare
  • Policy Consequences
  • Consequences for Congress’ Relationship with the President
  • Relationship with the Electorate

Political Science Partisan Polarization in the US Congress
Sean M. Theriault, Megan M. Moeller
  • LAST REVIEWED: 13 January 2014
  • LAST MODIFIED: 13 January 2014
  • DOI: 10.1093/obo/9780199756223-0088


The trend of polarization between the political parties in Congress is, perhaps, the most pronounced development in Congress since World War II. In the last few years, political scientists have described and analyzed this trend in a fairly comprehensive way. Indeed, the causes and consequences of partisan polarization have become a cottage industry among congressional scholars. The congresses after the 1964 election and into the 1970s were some of the least polarized in modern history. According to Keith Poole and Howard Rosenthal’s DW-NOMINATE, a statistic that summarizes voting in the House and Senate, the average Democrat was about 0.50 away from the average Republican in both the House and Senate. Because the total scale is 2 points, this gap represents about 25 percent of the entire scale. The infusion of Tea Party members in the 112th Congress and the losses suffered by the Blue Dog Democrats in 2010 only exacerbated the divide between the parties. In the 112th Congress (2011–2012), the divergence between the parties had more than doubled in the House to 1.07 and increased by more than 70 percent to 0.85 in the Senate. Nothing about the politics that the parties practice today suggests that the partisan polarization is going to slow down in the near future.

Review Articles

It took political scientists a long time to get interested in questions of party polarization, but once they became interested, a broad and deep literature developed. These review articles describe this vibrant literature. While Schaffner 2011 focuses almost exclusively on institutional polarization, Hetherington 2009 adds polarization within the electorate to the author’s analysis. Theriault and Moeller 2013 shows how the 2012 elections affected polarization in both arenas.

  • Hetherington, Mark J. “Review Article: Putting Polarization in Perspective.” British Journal of Political Science 39 (2009): 413–448.

    DOI: 10.1017/S0007123408000501

    Most scholars agree that polarization at the elite level not only exists, but is growing. There is more dispute about polarization in the mass electorate. Hetherington shows that the overall ideological mood of the American electorate has not appreciably changed, though the electorate has ideologically sorted itself.

  • Schaffner, Brian F. “Party Polarization.” In The Oxford Handbook of the American Congress. Edited by Eric Schickler and Frances Lee, 527–549. New York: Oxford University Press, 2011.

    The author documents the growing divide between the parties and describes the literature that developed around this divide. He also analyzes the consequences of this polarization, though he argues that political scientists can do much more work on this dimension.

  • Theriault, Sean M., and Megan M. Moeller. “The Effect of the 2012 Elections on Party Polarization.” In The American Elections of 2012. Edited by Janet M. Box-Steffensmeier and Steven E. Schier, 122–144. New York: Routledge, 2013.

    The authors show the consequences on party polarization as a result of the 2012 elections. They argue that the parties and the voters supporting them have not only ideologically polarized, but also racially polarized. Nothing in the results of the 2012 election suggests that polarization will decrease in the near future.

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