Consensus, Disorder, and Ideology on the Supreme Court

Ideological models are widely accepted as the basis for many academic studies of the Supreme Court because of their power in predicting the justices' decision-making behavior. Not all votes are easily explained or well predicted by attitudes, however. Consensus in Supreme Court voting, particularly the extreme consensus of unanimity, has often puzzled Court observers who adhere to ideological accounts of judicial decision making. Are consensus and (ultimately) unanimity driven by extreme factual scenarios or extreme lower court rulings such that even the most liberal and most conservative justice can agree on the case disposition? Or are they driven by other, nonattitudinal influences on judicial decisions? In this article, we rely on a measure of deviations from expected ideological patterns in the justices' voting to assess whether ideological models provide an adequate explanation of consensus on the Court. We find that case factors that predict voting disorder also predict consensus. Based on that finding, we conclude that consensus on the Court cannot be explained by ideology alone; rather, it often results from ideology being outweighed by other influences on justices' decisions.