CHARLESTON, S.C. – A moment that Newt Gingrich had long been hoping for and one that he had long been dreading collided Thursday when a new opening for him to rally conservatives around his candidacy was suddenly complicated when the second of his three wives stepped forward to say he had asked for an "open marriage."

As Gov. Rick Perry of Texas dropped out of the Republican presidential race and threw his support behind Gingrich, he declared, "Newt is not perfect, but who among us is?"

But after belatedly discovering that he had won the Iowa caucuses, Rick Santorum, Gingrich's rival for the role of conservative alternative to Mitt Romney, made a pointed appeal to evangelical voters, calling himself someone who "walks the walk and talks the talk."

Two days before the South Carolina primary, the Republican presidential campaign was upended by a torrent of developments from dawn to dusk that left Romney unsure of his footing.

He made a congratulatory call to Santorum after the Republican Party in Iowa wiped out his eight-vote margin and put Santorum ahead, but Romney's aides were so skittish that they insisted it was not a concession.

Gingrich was at center stage when the candidates opened their final debate before the primary, angrily denouncing questions about whether he had sought an "open marriage" and then aggressively taking on Romney and the other remaining candidates in a raucous confrontation about policy, conservative credentials and electability.

The cascading events shook the perception of inevitability surrounding Romney's march toward the nomination and left Gingrich with the simultaneous challenges of holding off Santorum, dealing with the baggage of his past and convincing Republicans that he is the most reliably conservative and electable candidate.

"I have no question that Newt Gingrich has the heart of a conservative reformer and the ability to rally and captivate the conservative movement," Perry said, a testimonial aimed at undercutting Romney's argument that he is ideologically consistent and the party's best hope of defeating President Barack Obama.

The question looming over the race was whether conservatives wary of Romney would follow Perry's lead and coalesce behind Gingrich or if they would remain split among Gingrich, Santorum and Rep. Ron Paul of Texas.

Perry's decision to leave the race and endorse Gingrich eclipsed what was shaping up as a big day for Santorum. News of the former Pennsylvania senator's newly minted victory in Iowa, by a margin of 34 votes, was drowned out almost as soon as it broke.

But Santorum's campaign was hoping to capitalize on the reminders of Gingrich's marital history that were pushed to the forefront when his second wife, Marianne Gingrich, told ABC News that Gingrich had once asked her to enter into an open marriage arrangement so he could continue seeing Callista Bisek, a congressional aide whom he later married.

As he campaigned in South Carolina, trying to seize upon the fresh endorsement from Perry, Gingrich tried to change the subject. He blamed ABC News for broadcasting an interview that he called "tawdry and inappropriate," but he did not directly respond to the account from his former wife, to whom he was married for 18 years.

"I'm not going to say anything about Marianne," Gingrich told reporters, referring questions to his two adult daughters from his first marriage. "I'm not getting involved."

The Santorum campaign, which is aggressively courting evangelical voters across South Carolina, received the endorsement on Thursday of James C. Dobson, an elder statesman of the evangelical movement.

At a weekend gathering of religious leaders in Texas, Dobson said Santorum's wife would make a better first lady than Callista Gingrich. Seeking to explain his views in a letter to Politico, he said it was "known that Callista Gingrich was his mistress for years."

Santorum said he was the only candidate still in the race who cared deeply about social conservative issues. He warned voters that Gingrich would "push them aside and focus on other things."

Gingrich welcomed the endorsement of Perry, and tried to use it to persuade conservative voters to join his candidacy. But a critical megaphone for news – talk radio – was consumed with a debate over whether his alleged request for an open marriage would harm him. It should not, said Rush Limbaugh, because he had at least asked permission.

The introduction of Marianne Gingrich into the campaign story line drove the conversation well before the interview was broadcast on Thursday on ABC News' "Nightline" program. The network released excerpts of the interview in the morning.

While Marianne Gingrich had told most of her story previously – much of the sentiment was contained last year in an article in Esquire – the comments took on added dimension because of the timing, Gingrich's resurgence in the polls and the impact of them being delivered on television. A former adviser to Gingrich said that his closest aides had frequently expressed concern that this day would come and upend his campaign.

Gingrich spent the day, as he has done at nearly every campaign stop since entering the race last year, with his wife, Callista, at his side. One audience member in Bluffton, S.C., quizzed Gingrich about his character and personal life, asking how voters would "come to grips with that if you are our nominee."

"Callista and I have a wonderful relationship," Gingrich said. "We knew we'd get beaten up, we knew we'd get lied about, we knew we'd get smeared, we knew there would be nasty attack ads," he said. "And we decided the country was worth the pain."

While Gingrich's standing has steadily improved in South Carolina, several polls show that his support lags among women. Strategists for rival campaigns were acutely focused on how the revelations would influence women's votes here on Saturday.

State Rep. Wendy K. Nanney, an evangelical Christian who represents Greenville, said her support for Gingrich would not waver because of it. She said that when she first met with Gingrich to discuss her support, "I asked him directly point blank, 'How do I get past your history?' "

"He was very honest," she said. "He said, 'I admit I was wrong, I did wrong, but I have asked forgiveness and I have moved forward and I have made some significant changes in my life, and I am a different person now.' "

LaDonna Ryggs, chairwoman of the Spartanburg County Republican Party, said she had been gauging reaction from women in one of the most conservative areas of the state.

"Divorces are never pretty, and I think that's pretty much what you're hearing from the ones who want to support him no matter what," Ryggs said. "If they do switch their minds on him, those votes are probably going to Santorum. I can't imagine them going anywhere else."

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