Dynamic estimation of ideal points for the US Congress

Theories of candidate positioning suggest that candidates will respond dynamically to their electoral environment. Because of the difficulty of obtaining “bridge votes”, most existing approaches for estimating the ideal points of members of Congress generate static ideal points or ideal points that move linearly over time. We propose an approach for dynamic ideal point estimation using Project Vote Smart’s National Political Awareness Test to construct bridge votes. We use our dynamic estimates to measure aggregate change, to measure individual-level change, and to study the institutional and structural factors that explain the changing positions of House candidates and members of Congress. We demonstrate that while the Republican Party has been selecting increasingly extreme candidates, Democratic incumbents have become more extreme while in office. We also find that the congruence between elected members of Congress and their constituents is mostly explained by the selection as opposed to the responsiveness of the candidate. Nonetheless, we find evidence of dynamic responsiveness of incumbents in specific circumstances. We find that competitiveness, midterm elections, and sharing the president’s party affiliation are associated with greater responsiveness. Conversely, retirement is not associated with a change in responsiveness. We find no evidence of responsiveness of challengers. Finally, we find that close elections draw challengers who are more in line with the district’s ideology.