Though retrospectiveperformance evaluations are now widely appreciated as a major influence on voting in general elections, their influence in presidentialprimaries has rarely been noticed. U sing exit polls conducted by major media organizations over the last nine election cycles, this article shows that retrospective voting is an important, indeed dominant, factor in two types of situations: when an incumbent president is running for reelection, and when an incumbent vice president is seeking to become his party's next presidential candidate. Thisfinding, inturn, helps explain two significant institutional features of the contemporary presidential nomination process: why most recent presidents have been renominated without much difficulty, and why the vice presidency has become such a good launching pad for presidential candidacies. How do voters make reasonably intelligent voting decisions, given that most of them are not terribly interested in politics, follow it only intermittently, and therefore do not have a great deal of information about the candidates and their issue positions? Political scientists have developed a number of answers to this question, but perhaps the most commonly invoked is the notion of retrospective voting. According to this theory, voters are less concerned with a candidate's or party's promises about future policy than with their past performance in office, particularly their success or failure in achieving such hard, tangible outcomes as peace and prosperity. Whereas information about campaign promises is costly to acquire and difficult to evaluate, most citizens develop relatively solid perceptions about the performance of an incumbent officeholder or administration simply by going about their normal lives and paying a minimal amount of attention to the news. The body of scholarly work bearing out the general theory of retrospective voting is, by now, quite large. The two most influential statements are V. O. Key's The Responsible