The Legislative Success of “Giant Killers” in the U.S. House

Monday, November 3, 2025

In modern congressional elections, fewer than 10% of candidates who run against sitting members of Congress win and yet they comprise as much as 30% of the House in any given congress. In this forthcoming paper in Political Science Quarterly, Sean Theriault, Professor at The University of Texas at Austin and Center for Effective Lawmaking (CEL) Faculty Affiliate, along with Jared Hrebenar and Isabel Reyna, examine the legislative effectiveness of those relatively rare challengers who knock off incumbents. The authors name them “Giant Killers,” and find that during the early part of their House careers they are 43% more effective than those who first join the House by winning an open seat. The authors suspect that the coalition-building skills that a candidate needs to win a difficult race against an incumbent may be similar to and correlated with the coalition-building skills needed to be legislatively successful. The CEL’s Legislative Effectiveness Scores were used for part of the research conducted for this paper, which itself is based on a CEL working paper on the topic.

To learn more, read the full report here.