Are Supreme Court Nominations a Move-the-Median Game?

Abstract

We conduct a theoretical and empirical re-evaluation of move-the-median (MTM) models of Supreme Court nominations. We develop a generalized MTM framework that encompasses the major models in the literature, which allow us to generate robust predictions that hold across all model variants. We then use advances in measurement and scaling to place presidents, senators, justices and nominees on the same scale, allowing us to conduct direct tests of the theory's predictions. We find weak support for MTM-theory. In particular, we find that senators have been much more accommodating of the president's nominees than MTM-theory would suggest -- as a result, many nominees have been confirmed when the theory predicted they should have been rejected. These errors have often been consequential, as presidents have selected many nominees who are much more extreme than MTM-theory would predict. These results raise serious questions about the adequacy of MTM-theory for explaining Supreme Court confirmation politics.