The top Republican in the Senate served notice on President Barack Obama Tuesday that the GOP won't rubber-stamp his choice to succeed the retiring Justice David Souter.

"The president is free to nominate whomever he likes," said Senate Minority Leader Mitch McConnell, R-Ky. "But picking judges based on his or her perceived sympathy for certain groups or individuals undermines the faith Americans have in our judicial system."

McConnell's Republicans are turning to a conservative Southerner as their point man on Obama's nominee, signaling that they won't shy away from a protracted fight despite risks of being cast as obstructionist.

Sen. Jeff Sessions' ascension as the top Republican on the Senate Judiciary Committee comes more than 20 years after the panel rejected him for his own federal judgeship during the Reagan administration over concerns that he was hostile toward civil rights and was racially insensitive.

Coincidentally, Sessions, R-Ala., replaces Sen. Arlen Specter of Pennsylvania, a moderate who was one of just two Republicans in 1986 to oppose Sessions as a U.S. district court judge. Specter left the GOP last week to become a Democrat, creating the vacancy atop the committee just as Justice David Souter announced his retirement.