Justice O’Connor’s departure from the Supreme Court in January 2006 left Justice Kennedy as the sole “swing” voter. Political scientists often to refer to a swing voter as a “pivotal voter” or the “median voter” because in theory, the pivotal voter’s vote provides a sufficient condition for rendering a collective outcome favored by the median voter. Kennedy leans toward the conservative side of the ideological spectrum (see below) but has joined the liberal justices in some high profile cases.
Kennedy’s swing vote status on the Court has been highlighted by commentators in the context of the replacement for Justice Stevens. It is important to remember that the appointment of Elena Kagan would not transform the ideological balance of the Court (assuming Kagan would not turn out to be more conservative than Kennedy once on the Court). Replacing Stevens with Kagan leaves Justice Kennedy as the swing voter on most issues. Thus, in the run-up to the Kagan announcement, many liberals emphasized the importance of replacing Justice Stevens with someone who would be able to influence Kennedy. As noted by Darren Hutchinson, many argue that Kagan provides the perfect fit (see here as well), given her track record for reaching out to conservatives and seeking to form consensus and coalitions across the ideological divide. Political scientist and Supreme Court scholar Paul Wahlbeck, who has done extensive research on collegial interaction and influence within the Court, forecasts that Kagan’s capacity for wielding influence will be limited. Moreover, in a recent post, I suggested that Kennedy had “become more solidly aligned with the four more staunch conservatives.” Jonathan Adler took issue with my generalization, pointing out cases — such as Mass v. EPA, Boumediene, Wyeth, and Kennedy v. LA. — that contradicted my claim.
I thought I would bring some data to bear on these topics, particularly examining Justice Kennedy’s voting agreement history with the liberal and conservative wings of the Court. The data offer a generalized, empirical foundation to Kennedy’s swing vote status, offer more fine-grained conclusions than the assertion I made about Kennedy (that Jonathan Adler corrected), and offer something of a glimpse of what we can expect in the future from Justice Kennedy. All of the data reported and examined here come from the Supreme Court Database.