Donors, Primary Elections, and Polarization in the United States

I examine the influence of partisan donors on the district-level ideological polarization of congressional candidates in the United States. I use data from 2002-10 U.S. House elections, which provide for the placement of major party primary winners on the same ideological dimension as their primary, general election, and partisan donor constituencies. Using this unique data set, I find strong evidence that the influence of donors in nominating contests is a source of polarization in the United States. House nominees are more responsive to their donor constituencies than either their primary or general electorates. I also find some evidence that the lack of general election competition affects nominee extremity. In safer districts, Democratic incumbents appear more responsive to donors. However, Republican donors seem to demand proximity regardless of district competitiveness. Overall, the polarizing effects of donor constituencies dominate any moderating effects, resulting in ideologically extreme nominees and, ultimately, members of Congress.