This data brief from the Unite America Institute, authored by Joseph Cerrone, analyzes Catalist voter-file data to examine who actually decides Congressional elections given that the vast majority of U.S. House races are effectively settled in party primaries. It finds that the small slice of voters who turn out in primaries skews markedly older, more partisan, and less representative of independents and moderates than the electorate as a whole, with liberals and conservatives overrepresented relative to their share of the population. The brief argues this mismatch between primary electorates and the general public helps explain why elected officials often appear more polarized than their constituents.