Ex-wife said she could destroy Newt Gingrich campaign. Will she?

Until now, Newt Gingrich’s troubled marital past has been airbrushed in the 2012 presidential race. If mentioned at all, it’s referred to as “baggage.”

That changes with ABC’s decision to air an exclusive interview with the former speaker’s second ex-wife on Thursday night, just two days before the South Carolina primary.

In a clip of the interview, released in advance of the broadcast, Marianne Gingrich tells “Nightline” that her then-husband “asked me to have an open marriage ... and accept the fact that he has someone else in his life.”

“I refused,” she said, in her first television interview since the couple’s divorce in 2000.

The interview hits just as the Gingrich campaign is gaining on the front-runner, former Gov. Mitt Romney. With a lift from a strong performance in Monday’s GOP presidential debate, Mr. Gingrich has surged to No. 2, within 10 points of Mr. Romney. Adding to the momentum is Texas Gov. Rick Perry’s decision, announced Thursday, to pull out of the GOP presidential race and back Gingrich.

But as in Iowa, the surge could stall or be reversed by a spike of negatives. In Iowa, Gingrich’s momentum was derailed by $3.5 million in negative campaign ads by a “super political-action committee” backing Romney.

The issue now is whether an interview with an ex-wife can have the same impact.

“People are looking for some non-Romney person, and Gingrich is emerging because of how well he did in the debate,” says David Woodard, a political science professor at Clemson University in South Carolina and author of “The America That Reagan Built.” “But he's got two hours with the ex-wife on national TV tonight, and there's nothing like a woman scorned to take the wind out of your sails.”

So far, the Gingrich campaign has avoided responding in kind. “Intruding into family things that are more than a decade old is simply wrong,” said Gingrich, in an interview on NBC’s “Today” show on Thursday morning.

In a letter to ABC executives, Kathy Lubbers and Jackie Cushman, Gingrich’s daughters from his first marriage, criticized the network for opting to run such an interview at this time.

“ABC News or other campaigns may want to talk about the past, just days before an important primary election. But Newt is going to talk to the people of South Carolina about the future,” they wrote. “We are confident this is the conversation the people of South Carolina are interested in having.”

“Things are crazy right now, but couldn’t be going better,” said Gingrich campaign manager Michael Krull, in a fundraising appeal released Thursday afternoon. “Bottom line is, we’re surging and in position to win South Carolina.”

It all turns on how South Carolina GOP primary voters digest two events Thursday night: another debate, where Gingrich is expected again to do well, and the televised interview with his former wife, where he is not. Sixty percent of likely GOP primary voters in South Carolina describe themselves as socially conservative.

Marital infidelities, past or present, aren’t lethal in politics. But how candidates deal with them can be. Responding to rumors of infidelity, former Sen. Gary Hart challenged the press to “follow me,” then dropped out of the 1988 presidential race less than a week later, after The Miami Herald substantiated the rumors. Sex-related scandals also clouded presidential bids of Sen. John Edwards (D) of North Carolina in 2008 and, most recently, GOP hopeful Herman Cain, who suspended his campaign on Dec. 3.

By contrast, Gingrich’s infidelities have been public record for decades. But the interview puts a new face on it – and new details – just as the candidate is vying for social conservative voters, who place importance on issues such as same-sex marriage and family values.

“There’s an element of hypocrisy with Mr. Gingrich that’s hard for people to take,” says Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington (CREW). Weathering sex-related scandals are “much harder when you have been claiming the mantle of family values,” she adds.

In a 1995 Vanity Fair interview, then-wife Marianne Gingrich quipped that if she didn’t support Gingrich’s decision to run for president, “I just go on the air the next day and I undermine everything.... I don’t want him to be president, and I don’t think he should be.”

In a sense, Thursday night’s interview is an unexpected test of that boast. “The Marianne Gingrich interview tonight may have an impact” on Newt Gingrich's candidacy, says Matt Towery, a former Gingrich campaign chairman and co-author of “Mean Business: The Insider's Guide to Winning Any Political Election.”

“I knew Marianne, I knew their marriage, and I can tell you definitively it was broken from the start,” he adds. “Both of them, without getting into specifics, have things they need to be really sorry about.”