What Happens When Extremists Win Primaries?

This article studies the interplay of U.S. primary and general elections. I examine how the nomination of an extremist changes general-election outcomes and legislative behavior in the U.S. House, 1980-2010, using a regression discontinuity design in primary elections. When an extremist-as measured by primary-election campaign receipt patterns-wins a coin-flip election over a more moderate candidate, the party's general-election vote share decreases on average by approximately 9-13 percentage points, and the probability that the party wins the seat decreases by 35-54 percentage points. This electoral penalty is so large that nominating the more extreme primary candidate causes the district's subsequent roll-call representation to reverse, on average, becoming more liberal when an extreme Republican is nominated and more conservative when an extreme Democrat is nominated. Overall, the findings show how general-election voters act as a moderating filter in response to primary nominations.