Over the past few decades, near-universal reelection of congressional incumbents in the United States has spawned scholarly interest in, as well as public concern about, the potential for erosion of competition and representation. When the deck seems to be stacked in favor of one set of candidates relative to another, the integrity of the democratic process is threatened. A central finding that has emerged in scholarly studies is that who wins elections often depends on who runs. As the inimitable congressional scholar Gary Jacobson has put it, "you can't beat somebody with nobody." In this...