Partisanship and incumbency in presidential elections

Party identification is a standard part of our understanding of presidential voting, but the effects of presidential incumbency on presidential voting have not been recognized in most voting models. Democratic candidates in the twentieth century received 10 percent more of the two-party vote when Democratic incumbents were running for reelection than when Republican incumbents were running. National Election Studies surveys show that the effect of incumbency varies with individual partisanship, with the greatest effect, as expected, among independents. Opposition party identifiers defect at a higher rate than incumbent party identifiers when the incumbent is running for reelection. Even after controlling for retrospective and prospective economic voting, a 6 percent effect is found for incumbency. Incumbency thus conditions the impact of partisanship on presidential voting.