Scholars have focused on elite-level and mass-level changes to explain partisan polarization in Congress. This article offers a candidate entry explanation for the persistence of polarization and the rise in asymmetric polarization. The central claim is that ideological conformity with the party-what I call Party Fit-influences the decision to run for office, and I suggest that partisan polarization in Congress has discouraged ideological moderates in the pipeline from pursuing a congressional career. I test this hypothesis with a survey of state legislators and with ideology estimates of state legislators who did and did not run for Congress from 2000 to 2010. I find that liberal Republican and conservative Democratic state legislators are less likely to run for Congress than those at the ideological poles, though this disparity is especially pronounced among Republicans. The findings provide an additional explanation for recent patterns of polarization in Congress. This article contributes to the polarization literature by offering a candidate entry explanation that highlights ideological variation in the types of candidates who run for Congress.The central claim is that ideological conformity with the party's ideological reputation-what I call Party Fit-influences the decision to run for office. A party's ideological reputation conveys information about the type of candidate that belongs in the party, and potential candidates draw on this reputation to determine if they can achieve their electoral and policy goals and to decide whether to run for office. The Party Fit hypothesis suggests that in the contemporary political context, partisan polarization in Congress has discouraged ideological moderates in the political pipeline from pursuing a congressional career. I test this hypothesis with survey data of the perceptions of state legislators (Maestas et al. 2006;Stone et al. 2004) article focuses on the self-selection mechanism. However, the argument does not preclude a role for parties, and it is likely that party recruitment also shapes perceptions of Party Fit. In addition, the theoretical expectations apply to both incumbent and non-incumbent candidates, but because replacement processes have been central to the rise in polarization, I focus on the latter, and more specifically, on non-incumbents who are well situated to run for Congress.There are many reasons to expect that potential candidates rely on the party's reputation to determine if they can achieve their electoral and policy goals (Fenno 1973; Mayhew 1974). 3 First, potential candidates draw on this reputation to estimate their likelihood of winning. Sniderman and Stiglitz (2012) show that candidates receive a reputational premium if they take a 3 Potential candidates can learn about the party's reputation through a variety of ways, such as polls, the media, and past candidates, but the ideological makeup of the party delegation is the best measure of the party's reputation. What is important is that this reputation provides diffe...