From the New York Times, In Supreme Court Clerks’ Careers, Signs of Polarization

Earlier studies have shown the rise of ideological hiring of clerks by the justices. In recent years, the more conservative justices have overwhelmingly hired clerks who had worked for appeals court judges appointed by Republicans. The more liberal justices did the opposite, but a little less consistently.

The new study, published last month in The Vanderbilt Law Review and summarized in the autumn issue of The Green Bag, collected data from 1882 through 2006, which means it did not consider information about clerks for the most recent additions to the court, Chief Justice John G. Roberts Jr. and Justices Samuel A. Alito Jr. and Sonia Sotomayor.

Before the 1990s, the study found, all sorts of former clerks used to serve in the government under all sorts of administrations.

That seemed to change in the Clinton years. The Clinton administration hired 96 former clerks, but only 16 percent of them came from the chambers of the four most conservative justices — Chief Justice William H. Rehnquist and Justices Antonin Scalia, Clarence Thomas and Anthony M. Kennedy.

Of the 89 former clerks hired by the administration of George W. Bush, on the other hand, 68 percent came from those four chambers.

“The only other justice who provided five or more clerks for President Bush was the fifth justice who cast a vote in his favor in Bush v. Gore,” the study said, referring to former Justice Sandra Day O’Connor, whose chambers provided eight additional clerks.