Winnable open primaries are the gateway to the U.S. House of Representatives. Most members of Congress gain their seats by first winning their party’s nomination in a district where the incumbent is retiring. Because most districts strongly favor one one party or the other, the winner of the favored party’s primary often has an easy time winning the general election.

Despite their critical role in shaping the U.S. House, we know little about House primaries. Political scientists often assume they are similar to general elections — despite the absence of party as a cue voters can use to distinguish candidates and (often) the presence of more than two candidates. Or we assume that House primaries are similar to presidential primaries, which take place over months, receive substantial media attention, and lead to general elections that are always strongly contested by both sides. House primaries are different from other, better-studied, kinds of election, in ways would seem to make a difference.

The Parties on the Ground project seeks to establish basic empirical understanding of winnable open House primaries from the perspective of on-the-ground participants. We studied all winnable open seat nominations in the 2013-14 electoral cycle, including special elections related to seats that became open mid-session. Our work is documented here.

Click “Supplemental Material”  to see the Online Appendix for “Groups, Parties and Policy Demands” in Accountability Reconsidered: Voters, Interests and Information in US Policymaking (edited by Charles M. Cameron, Brandice Canes-Wrone, Sanford C. Gordon, Gregory A. Huber, Cambridge Univeristy Press 2023.)