Ranking the Politics of Supreme Court Justices

Supreme Court in Washington, D.C.

Some of the results of the authors' analysis are familiar, if not reassuring. The study demonstrates, for example, that Supreme Court justices, in spite of their reputation for impartiality, really do seem to vote along ideological lines. With only a few exceptions, for 70 years, Republican-appointed justices have tended to vote conservatively, and justices appointed by Democrats have tended to vote liberally. "A lot of this just confirms what everybody already knows," says Landes.

But the paper reveals more than that. For one thing, it demonstrates just how much every vote on the Supreme Court counts—particularly, it seems, when the court is leaning conservative. The authors were surprised to find a dramatic pooling effect over the years every time a conservative justice joined the court. "The larger the fraction of justices appointed by Republican presidents," they write, "the more conservatively each Justice [votes]." With McCain promising to nominate conservatives, this finding appears to have real significance today: The more conservatives join a conservative court, the more conservative each justice gets.

The same thing doesn't appear to be true, curiously, for left-leaning judges. The authors find that the court's liberal justices are driven to vote more ideologically not when their numbers grow but when they begin to drop. The fewer justices there are on the court appointed by Democratic presidents, in other words—meaning the more outnumbered the liberal justices are—the more liberal those justices get. Even when the majority shifts only a small amount, from 5-4 liberal to 5-4 conservative, liberal justices tend to vote more liberally about 3 percent of the time. "There's a real polarization effect," says Landes.

Today's court, it seems, appears to be in just this situation, with increasingly ideological justices moving toward the ends of the political spectrum. But there may be a solution already in the making: The political atmosphere surrounding judicial nominations, the authors point out, has a dramatic effect on not only what kinds of judges are nominated but how they vote once they're on the bench. The more Republicans there are in the Senate, according to the study, the more conservatively the justices they appoint tend to vote. But over the years, when the number of GOP senators drops—something many political experts think may be likely this fall—so, too, does the career conservative rating of the justices they appoint to the bench. "It's an interesting finding," says Landes. "There's some real predictive power here. You can determine a lot about how each justice is going to vote based on the political party of the president who appointed them and the composition of the Senate."

This fall's election may be about many things, but the presidential candidates aren't the only ones vying for the power to change the court. Each Senate race, too, may have an impact on what kinds of justices will take a seat on the bench.