“You can’t possibly delegate as much as the justices do without turning over a degree of responsibility,” said Lawrence Baum, a political scientist at Ohio State who has published empirical studies of Supreme Court clerks.

Influencing the Law

Indeed, the polarization among law clerks has had consequences for the development of the law, a 2008 study published in the DePaul Law Review found. The presence of clerks who identified themselves as Democrats made liberal votes from the justices for whom they worked more likely, the study found. The opposite was true, too.

A handful of federal appeals court judges known as feeder judges are gatekeepers. J. Michael Luttig, for instance, produced more than 40 Supreme Court clerks in his 15 years on the federal bench, with 33 of them going to work for Justices Thomas or Scalia. Mr. Luttig, now general counsel of the Boeing Company, said the justices’ overall hiring practices reflected a fundamental shift.

“As law has moved closer to mere politics, political affiliations have naturally and predictably become proxies for the different political agendas that have been pressed in and through the courts,” Mr. Luttig said. “Given this politicization, it should come as no surprise to learn that the more liberal judges tend both to hire clerks who would self-describe themselves as Democrats and to hire clerks from other judges who would likewise self-describe themselves as Democrats, and vice versa for the more conservative judges.”

But ideological orthodoxy can dampen the robust discussions in chambers that clarify issues and shape rulings. Justice Scalia for instance used to seek out candidates from the opposite ideological camp when he served on a federal appeals court in Washington and in his early years on the Supreme Court.

“He made it a point of telling me that I was his token liberal,” said E. Joshua Rosenkranz, who clerked for Justice Scalia in 1986, his last year on the appeals court. “To his credit, I’m sure it was largely because he wanted to be sure he always heard the arguments against the positions he was taking.”

The politics do not stop when clerks leave the court. Though a clerkship is a ticket to a law firm job that can include a $250,000 signing bonus, many former clerks take positions consistent with their former bosses’ ideological leanings in the legal academy, the government and elsewhere.