The retirement of Justice Anthony Kennedy and nomination of conservative Brett Kavanaugh to replace him is poised to give Republicans a more reliable majority on the Supreme Court. But a 5-4 majority is a narrow one. A Democratic victory in the 2020 presidential election coupled with the death of a single Republican appointed justice would produce a reversal in power on the Court. The current state begs the question: precisely how likely are Democrats to regain the majority?
Despite the complexities of the legal and political processes that produce Supreme Court candidates, this question is surprisingly approachable statistically. The central variables involved are not from the domain of legal theory or constitutional interpretation, but rather from areas familiar to a statistician: life expectancy, behavioral preferences, and election projection. By consulting actuarial tables, the record on judicial retirements, and the history of presidential election results, I have endeavored to construct a quantitative understanding of the likelihood of changes of control on the Supreme Court.