“If Roberts stays right where he is now and he becomes the median, it could pull the court quite a bit to the right,” said Lee Epstein, a law professor and political scientist at Washington University in St. Louis. “He will prefer to try to form a coalition with the other conservatives, although he will occasionally side with the liberals.”

Justice Sandra Day O’Connor became more moderate when Justice William J. Brennan Jr. and Justice Thurgood Marshall left the court, said Michael C. Dorf, a Cornell Law School professor who clerked for Justice Kennedy, and Justice Kennedy likewise moved to the center when Justice O’Connor departed.

“It could manifest in compromise positions in his taking substantively more moderate stances on issues,” Mr. Dorf said. “He might want to go slowly before taking an abortion case or an affirmative action case, or a same-sex marriage case to potentially overturn Justice Kennedy’s handiwork.”