The Incumbency Advantage in U.S. Primary Elections1

Using a new data set, we estimate the magnitude of the incumbency advantage in direct primary elections between 1910 to 2000. We ̄nd that the incumbency advantage, as estimated by the sophomore surge, was above 5 percentage points in primary elections even in the ̄rst decades of the twentieth century. The sophomore surge in primary elections grew to approximately 15 percentage points by the end of 1990s. The growth of the sophomore surge in primary elections occurred at least a decade prior to the growth of the sophomore surge in the general elections. We ̄nd some evidence that the structure of intra-party competition a®ects the incumbency advantage. Speci ̄cally, examining southern and border states, we ̄nd that the sophomore surge was signi ̄cantly smaller in states with persistent intra-party factions.