A Spatial Model of Roll Call Voting: Senators, Constituents, Presidents, and Interest Groups in Supreme Court Confirmations

We test a spatial model of Supreme Court confirmation votes that examines the effects of (1) the ideological distance between senators' constituents and nominees, (2) the personal ideologies of senators, (3) the qualifications of the nominee, (4) the strength of the president, and (5) the mobilization for and against nominees by interest groups. The data consist of the 1,475 individual confirmation votes from the 1955 nomination of John Harlan until the 1987-88 nomination of Anthony Kennedy (voice votes excluded). All of the above factors significantly affect confirmation voting. The model explains 78% of the variance in senators' decisions, predicts 92% of the individual votes correctly, and predicts all of the aggregate outcomes correctly.