Rick Santorum, Mitt Romney, Newt Gingrich, Ron Paul

Republican presidential candidates, from left, former Pennsylvania Sen. Rick Santorum, former Massachusetts Gov. Mitt Romney, former House Speaker Newt Gingrich and Rep. Ron Paul, R-Texas, take part in a Republican presidential debate Monday Jan. 23, 2012, at the University of South Florida in Tampa, Fla, as moderator Brian Williams of NBC News listens. (AP Photo/Paul Sancya)