Accounting for Protest Voting in the U.S. Congress

Abstract Members of the majority party in Congress sometimes vote against bills that they prefer over the status quo. We estimate a model of congressional roll-call voting that allows for this kind of non-ideological protest voting. We find that protest voting has significant implications for roll-call-based estimates of ideology and other analyses that rely upon them. For example, a traditional item response theory model curiously identifies members of the Squad as relatively moderate Democrats, but our protest-voting-adjusted scores identify them as the most liberal members of Congress. We also find that previous studies may have underestimated responsiveness, the effects of ideology in elections, the utility of non-roll-call-based measures of ideology, and the increase in congressional polarization. Although the implications for most substantive applications are likely modest, our analyses suggest that future researchers can better measure legislative ideology by accounting for a small number of non-ideological votes.