The race for the U.S. Republican presidential nomination narrowed to four contenders Thursday, who sparred in a volatile debate in South Carolina ahead of Saturday's primary in the key state.

Former U.S. House Speaker Newt Gingrich, Texas Congressman Ron Paul, former Massachusetts governor Mitt Romney and former Pennsylvania senator Rick Santorum argued over jobs, health care, and leadership.

Gingrich turned angry when questioned at the start of the debate about allegations by his ex-wife that he asked for an “open marriage” in 1999 to accommodate an extramarital affair.

He said flatly that the story is false, and he attacked what he described as the “elite” news media, calling it destructive, vicious and negative.

Romney, in turn, defended himself from accusations that he cut jobs when he headed an investment firm that bought other companies. He said he actually helped companies create jobs, and said he would not apologize for being a successful businessman.

Santorum and Romney criticized Paul for his plans to cut military spending, while all the candidates criticized President Barack Obama's health care plan and called for a crackdown on illegal immigration.

Just hours before the debate Thursday, Texas Governor Rick Perry dropped out of the race after poor showings in the Iowa caucuses and New Hampshire primary. He then endorsed Gingrich as the Republican candidate.

South Carolina holds its primary Saturday. The latest polls show Romney as the front runner, but support for Gingrich is rising.

Also Thursday, Rick Santorum's candidacy got a boost when Republican officials in the state of Iowa said he won the most votes in the state's January 3 caucuses. Initially, Iowa Republican officials said Romney won the caucuses by eight votes, and Santorum, a social conservative, came in second.