Incumbency, redistricting, and the decline of competition in US House elections

Competition in U.S. House elections has been declining for more than 50 years and, based on both incumbent reelection rates and the percentage of close races, the 2002 and 2004 House elections were the least competitive of the postwar era. This article tests three hypotheses that attempt to explain declining competition in House elections: the redistricting hypothesis, the partisan polarization hypothesis, and the incumbency hypothesis. We find strong support for both the partisan polarization hypothesis and the incumbency hypothesis but no support for the redistricting hypothesis. Since the 1970s there has been a substantial increase in the number of House districts that are safe for one party and a substantial decrease in the number of marginal districts. However, this shift has not been caused by redistricting but by demographic change and ideological realignment within the electorate. Moreover, even in the remaining marginal districts most challengers lack the financial resources needed to wage competitive campaigns. The increasing correlation among district partisanship, incumbency, and campaign spending means that the effects of these three variables tend to reinforce each other to a greater extent than in the past. The result is a pattern of reinforcing advantages that leads to extraordinarily uncompetitive elections.