Primary elections in the United States have been understudied despite their influence on candidate selection. Using new data and ideal point estimation, this research examines how primary electorates shape party nominees' ideologies. We analyze district-level data from the Cooperative Congressional Election Study to reveal that Republican primary electorates favor more extreme candidates compared to general election voters. In contrast, Democratic primary electorates show less divergence in ideological preferences when selecting their party's nominee for Congress.
