What are the consequences of one-party politics for the behavior of individual citizens? How do these individual-level consequences serve to perpetuate one-party dominance? One important mechanism of this self-perpetuation is the institutionally disadvantaged position of the minority party, particularly with respect to the participatory incentives attached to primary election participation. Our argument is as follows: (1) The best way for a minority partisan to maximize her influence in a primary election is often to vote the majority party's primary ballot. But (2) as a result of such crossover voting the minority party loses an important manifestation of support – participation in its own primary election. And thus (3) the minority party demonstrates a level of support that greatly exaggerates the extent to which it is a minority. Furthermore, (4) many individuals who participate in majority party affairs by voting in majority party primaries are likely to develop loyalties to the majority party.