Center for the Study of Democracy

Using the Martin-Quinn ideology scores, we show that U.S. Supreme Court justices strategically respond to Supreme Court membership change. At the aggregate level, the Court moves to counter-balance the ideological change brought about by a new justice. The behavior is most prevalent in 1938-1948, which we call a period of “Constrained Liberalism” and 1975-1995, which we call a period of “Constrained Conservatism.” Counter-balancing is less prevalent throughout the 1950s – early 1970s when justices either ignored or amplified ideological shifts caused by the membership change (especially liberal shifts in 1960s). At the individual level, membership change in the conservative direction leads to a greater response from liberal justices while a change in the liberal direction leads to a greater response from the conservative justices. One implication of our results is that the prevalence of this counter-balancing reaction to membership change has a stabilizing effect on the aggregate ideology of the Supreme Court.