Santorum tries to shoulder past Romney, Gingrich in debate NEW: Santorum says Romney, Gingrich played "footsies with the left" Gingrich replies angrily to first question on ex-wife's allegations Editor's note: Tune in now for the CNN-Southern Republican Presidential Debate hosted by John King and follow it on Twitter at #CNNDebate. Charleston, South Carolina (CNN) -- Arguing that momentum was on his side after a delayed announcement of victory in Iowa, former Sen. Rick Santorum sought to weaken rivals Mitt Romney and Newt Gingrich with a series of direct attacks on the two front-runners in the last South Carolina debate ahead of the state's primary on Saturday. Santorum charged both Romney and Gingrich would be weaker opponents against President Barack Obama, saying neither could draw a contrast with the incumbent over health care policy. The former Pennsylvania senator called the Massachusetts health care plan passed while Romney was governor "an abject disaster" and said Gingrich has supported an individual mandate for 10 years. I've been fighting for health reform, private sector, bottom up, the way America works best, for 20 years. While these two guys were playing footsies with the left, Santorum said. The debate came at the end of a ground-shaking day that saw Santorum being declared winner of the Iowa caucuses more than two weeks after his apparent second-place finish to Romney and Texas Gov. Rick Perry dropping out of the race and throwing his support to Gingrich. It is the last matchup between the four candidates two days before Saturday's pivotal first in the South primary. Santorum repeatedly called Gingrich "grandiose" and warned primary voters the former speaker was not disciplined enough to run an effective general election campaign. "Grandiosity has never been an issue with Newt Gingrich," Santorum said. Romney responded with a full-throated defense of states' rights, while Gingrich said he could easily defeat Obama in a debate with a simple line: "I can say, you know, I was wrong and I figured it out. You were wrong and you didn't. Earlier an angry Newt Gingrich chastised CNN for starting off with a question about reports that he offered his then-second wife a choice of an open marriage or divorce when he revealed to her he was having an affair with the woman he later made his third wife. "To take an ex-wife and make it two days before the primary a significant question in a presidential campaign is as close to despicable as anything I can imagine," Gingrich told CNN Chief National Correspondent John King, the moderator of the debate. Gingrich's response elicited loud applause from the audience. Hours before the debate, ABC News and The Washington Post released interviews with Marianne Gingrich in which she alleged Gingrich asked for an "open marriage" before their divorce. Marianne Gingrich told The Washington Post that a day after he husband told her about his affair with Callista Bisek in May 1999, the former House speaker delivered a speech titled "The Demise of American Culture" to a group of Republican women in Pennsylvania. Gingrich said the story was false. The three other presidential candidates on the stage passed on the chance to criticize Gingrich over the allegations by his ex-wife. Four polls over the last two days show Romney's long-held lead in South Carolina nearly evaporating into single digits by the time the four took the stage, while Gingrich has surged into a virtual tie. Gingrich on Thursday grabbed a major endorsement when Perry announced he was backing Gingrich as he suspended his campaign. Santorum's campaign got a boost on Thursday when the Iowa GOP released the final certified results from its January 3 caucuses, which reversed Romney's eight-vote victory and instead determined that Santorum had won by 34 votes. And Rep. Ron Paul of Texas had a solid third-place finish in Iowa and a strong second-place finish last week in New Hampshire, but most political pundits saw his performance in Monday's debate in Myrtle Beach, South Carolina, as strained. And attacks by his rivals seemed to put the front-runner on his heels. Gingrich has been criticized by fellow Republicans for his attacks on Romney's venture capitalist past, which some were uncomfortable with because they saw it as an attack on the free market and thought it could be damaging in the general election. "Gingrich has all the charm and warmth of a chainsaw but right now, Republicans want to cut Washington to ribbons," said Alex Castellanos, a GOP strategist and CNN contributor, before the debate. As for Romney, with his numbers slipping, a strong performance was a must.