CHARLESTON, S.C. -- Mitt Romney’s aura of inevitability took a hit Thursday, just as the biggest threat to his campaign, Newt Gingrich, suddenly faced unwelcome questions about once asking his ex-wife for permission to have an “open marriage.”

To call Thursday the most turbulent day of an already volatile presidential primary would be an understatement. South Carolina suddenly is a neck-and-neck race between the two. And, as a result, Florida’s Jan. 31 primary looks like less of a cakewalk for Romney.

The morning began with Texas Gov. Rick Perry ending his struggling campaign and endorsing Gingrich. About the same time, Iowa certified results from its Jan. 3 caucuses, showing that — contrary to early reports about Romney barely winning — Rick Santorum finished with 34 more votes.

But Gingrich’s ability to capitalize on the one-two blow to Romney was buried by a sensational ABC News interview with Gingrich’s second wife, Marianne, who said he wanted an “open marriage” so he could continue an affair with his aide at the time, who eventually became his third wife.

Gingrich turned the weakness into a strength Thursday night at the CNN debate here when moderator John King tried to ask Gingrich about it.

“This story is false" Gingrich said. "I am frankly astounded that CNN would take trash like that and use it to open a presidential debate."

Gingrich got a standing ovation and “calls of Newt!” for bashing the "destructive, vicious, negative nature" of the news media.

"I am tired of the elite media protecting Barack Obama by attacking Republicans," he said. After Gingrich scolded CNN’s King, the other candidates refused to touch the issue.

But Gingrich has made family-values a part of his campaign. And just as he questions Romney’s business background, he’ll face questions about his past.

The ABC News report won’t go away, and supporters of his Republican opponents will likely play up Marianne Gingrich’s comments.

"He wanted an open marriage and I refused,” she told ABC News.

Gingrich and Romney are essentially tied, according to an average of five South Carolina polls released Wednesday and Thursday.

Romney, the frontrunner, was already waning before Thursday. Romney was 2-0 heading into South Carolina. But the re-counted Iowa ballots put him at 1-1.

Technically, there was no official winner of the Iowa caucuses because the party said it had not received results from eight of the state’s 1,774 precincts. Local party officials were supposed to submit forms by Wednesday summarizing the precincts’ total, but some never turned up by the deadline for certifying the election.

That makes Saturday’s primary winner crucial — especially in Florida, where the electorate is driven in large part by a television ad war.

"It’s the narrative that matters. The winner in South Carolina matters," said David "DJ" Johnson, a former Republican Party of Florida executive director and Florida adviser to Jon Huntsman’s now-scuttled campaign.

"Debates matter, too," Johnson said. “But it’s unclear how the Marianne story will play out.”

ABC’s Nightline aired the full report just after Thursday’s CNN debate.

Also, it’s unclear how much Perry will support Gingrich and whether his support really means much. Perry only garnered 6 percent of the vote in a CNN poll. His campaign appearances in South Carolina have been characterized by small, unenthusiastic crowds, and he was barely registering in recent Florida polls.