A Common-Space Measure of State Supreme Court Ideology

We introduce a new method to measure the ideology of state Supreme Court justices using campaign finance records. In addition to recovering ideal point estimates for both incumbent and challenger candidates in judicial elections, the method’s unified estimation framework recovers judicial ideal points in a common ideological space with a diverse set of candidates for state and federal office, thus facilitating comparisons across states and institutions. After discussing the methodology and establishing measure validity, we present results for state supreme courts from the early 1990s onward. We find that the ideological preferences of justices play an important role in explaining state Supreme Court decision-making. We then demonstrate the greatly improved empirical tractability for testing separation-of-powers models of state judicial, legislative, and executive officials with an illustrative example from a recent political battle in Wisconsin that ensnared all three branches.