The Electoral Origins of Polarized Politics

Data from the 2010 Cooperative Congressional Election Study are examined to determine the extent to which partisan polarization is a popular as well as an elite phenomenon. The evidence indicates that ordinary Americans as well as political elites divide consistently along party lines over a broad range of issues and legislative preferences. Partisan ideological divisions are not confined to the political class; they extend downward into the citizenry to the degree that people are actively involved in politics. The coincidence of partisan differences across issues results in a bimodal distribution of aggregate preferences among voters, showing that partisan sorting can by itself polarize the electorate even if sorted partisans do not adopt extreme positions on individual issues. The distribution of partisan preferences is even more sharply bimodal and polarized when the electoral constituencies of the congressional parties are compared, so the electoral process sustains elite polarization. Primary electoral constituencies tend to be even more extreme, particularly on the Republican side, deterring departures from party orthodoxy and thus movement toward the median voter.