Bargaining Power in the Supreme Court

How can we assess bargaining power within the Supreme Court? Do authorship and opin-ion assignment affect legal policy? We argue that fluidity, differences between a justice’s initial vote and final vote, can indicate the location of the Court’s majority opinion. Justices should be less likely to defect the happier they are with the majority opinion, and bargaining models make differing predictions for opinion location and the influences thereon. Therefore, these models can make different predictions for how opinion assignment will affect whether justices change their votes. We derive theoretical hypotheses from each model. Using multilevel probit regression and Supreme Court vote data, we show that power within the Court lies in the hands of opinion authors, and thus of the Chief Justices who pick them, as constrained by the need to maintain a majority coalition. We find evidence against three other major models of judicial bargaining (median monopoly, majority-median monopoly, and author monopoly). At the end of each Supreme Court term, there is much talk in the popular media of swing justices and whose “Court ” it is, particular when the locus of power seems to have changed. After an unusually extended period of stability, the ideological makeup of the Court has indeed shifted in recent years. Once Justice O’Connor retired in 2006 and Justice Alito took her place, the label of pivotal swing vote shifted from O’Connor to Justice Kennedy. In the 2006-7 term, Kennedy was in the majority in all 24 of the Court’s 5-to-4 decisions, and the media proclaimed the beginning of the “Kennedy Court. ” Despite a precipitous drop in 5-to-4 decisions in the 2007-08 term (from 2