According to many pundits and scholars, closed primary elections are a major contributor to the ideological polarization in Congress and state legislatures. By partitioning voters into two ideologically-sorted electorates, they argue, closed primaries incentivize candidates to adopt the positions of voters in their party rather than of their constituency as a whole. As a result, they elect representatives who consistently toe the party line and resist compromise. Advocates of reform, from academics like Morris Fiorina to practitioners like Arnold Schwarzenegger, therefore argue that replacing closed party primaries with a more open nominating process will reduce polarization and its offspring—gridlock and a noxious political atmosphere—by helping moderate candidates. Are these claims about the consequences of reform valid?
To shed further light on the consequences of this reform, we conducted a statewide experiment before California’s June 2012 primaries. As a result of a popular referendum, these elections replaced the closed party primaries with an open ballot that presented voters, regardless of party, with the same list of candidates. The top two vote getters advanced to the general election, thus allowing for a choice between two contenders from the same party. In a study sponsored by the Institute of Government Studies at UC Berkeley, we randomly assigned 2839 registered voters in U.S. House districts where moderate candidates faced more extreme candidates to one of two conditions for electoral choice: (1) the open ballot that would be used in the actual 2012 primary, or (2) the closed primary ballot that earlier elections employed.
For advocates of the reform, the results of this survey experiment are disappointing. If the open ballot did indeed help moderate candidates, they should have won more votes in the open-ballot condition than in the closed-ballot condition. But as shown in the scatterplot below, we find no such evidence: Moderate candidates for the House of Representatives fared no better under the top-two primary than they would have in closed party primaries. The vertical axis plots how much better (or worse) candidates performed among participants randomly assigned to the top-two ballot, while the horizontal axis plots candidate moderateness on a seven-point scale. The results fail to show the upward-sloping trend that advocates of primary reform argue we should see.