Congressional incumbency and the rise of split-ticket voting

Despite the general recognition that incumbency has influenced voters' deci sions to split their ballots for president and the House, past research has not focused on the specific magnitude of this effect and its responsibilit y for growing ticket-splitting in the United States. In this study, I find that incumbency was a powerful determinant of the step jump in ticket-split ting that occurred from the 1956-68 to 1972-92 periods. This is in contrast to the weak expansive force exerted by declining partisan intensity in the electorate. Incumbency's impact, however, was confined to districts where members of the losing presidential party run for reelection; in districts w ith campaigning incumbents of the winning presidential party, it made for o nly about the level of ticket-splitting that could be expected in open seat s.