“At any given time, the liberal bloc of the court has been able to peel away a justice from the conservative bloc,” Mr. Malcolm said. With a Justice Barrett, “the liberal bloc can peel one of those justices away, but…you still have a 5-4 majority for the conservatives.” Thus, a third Trump appointee, after Justices Neil Gorsuch and Brett Kavanaugh , could lock in conservative outcomes across the board.

Judge Barrett’s known views fall to the right of the two prior Trump appointees, and somewhat to the left of Justices Thomas and Alito, according to an analysis of judicial ideology by researchers at Washington University in St. Louis and the University of Michigan. As a result, the court’s “median justice,” currently Chief Justice Roberts, would shift rightward to Justice Kavanaugh, said one of the study’s authors, Lee Epstein , a political scientist and law professor at Washington University.

Still, once appointed to their life-tenured seats, some justices have deviated from their ideological paths. Justice Ginsburg’s predecessor, Justice Byron White, an appointee of President Kennedy, sometimes joined conservatives, for example in dissent from Roe. Justice David Souter, appointed by President George H.W. Bush, failed to perform an expected about-face from the liberal champion he succeeded, William Brennan.