WASHINGTON — Each year, 36 young lawyers obtain the most coveted credential in American law: a Supreme Court clerkship. Clerking for a justice is a glittering capstone on a résumé that almost always includes outstanding grades at a top law school, service on a law review and a prestigious clerkship with a federal appeals court judge.

Justice Clarence Thomas apparently has one additional requirement. Without exception, the 84 clerks he has chosen over his two decades on the court all first trained with an appeals court judge appointed by a Republican president.

That unbroken ideological commitment is just the most extreme example of a recent and seldom examined form of political polarization on the Supreme Court. These days the more conservative justices are much more likely than were their predecessors to hire clerks who worked for judges appointed by Republicans. And the more liberal justices are more likely than in the past to hire from judges appointed by Democrats.

Each justice typically hires four clerks a year. Since Chief Justice John G. Roberts Jr. joined the court in 2005, Justice Antonin Scalia has not hired any clerks who had worked for a judge appointed by a Democratic president, and Justice Samuel A. Alito Jr. has hired only two. At the other end of the ideological spectrum, only four of Justice Ruth Bader Ginsburg’s clerks on the Roberts court came from judges appointed by Republicans. The early data on President Obama’s two appointees, Justices Sonia Sotomayor and Elena Kagan, show a similar pattern.

Full story: Supreme Court Clerks, Like Justices, Lean Left or Right – NYTimes.com