Who Punishes Extremist Nominees? Candidate Ideology and Turning Out the Base in U.S. Elections∗

Political observers, campaign experts, and academics alike argue bitterly over whether it is more important for a party to capture ideologically moderate swing voters or to encourage turnout among hardcore partisans. We speak to this debate by examining the link between the ideology of congressional candidates and the turnout of their parties’ bases in U.S. House races, 2006–2012. Combining a regression discontinuity design in close primary races with survey and administrative data on individual voter turnout, we find that extremist nominees suffer electorally, largely because they decrease their party’s share of turnout in the general election, skewing the electorate towards their opponent’s party. Along with shedding light on questions concerning the interplay of parties, voters, and candidates, the results help address the debate over swing voters and turning out the base. For our sample of elections, turnout appears to be the dominant force in determining election outcomes, but it advantages ideologically moderate candidates because extremists activate the opposing party’s base more than their own. ∗For helpful discussion, the authors thank Avi Acharya, Jim Fearon, Anthony Fowler, Stephen Pettigrew, Ken Shotts, Brad Spahn, and participants of the MIT American Politics Conference. For data, the authors thank Shigeo Hirano and Jim Snyder. For guidance using voter file data, the authors especially thank Brad Spahn. All remaining errors are the authors’ sole responsibility. †Andrew B. Hall is an Assistant Professor in the Department of Political Science at Stanford University ([email protected], http://www.andrewbenjaminhall.com). ‡Daniel M. Thompson is a Ph.D. Student in the Department of Political Science at Stanford University.