On the most tumultuous day of the GOP primary to date, Rick Perry dropped out and endorsed Newt Gingrich; Gingrich’s former wife went public with private details about her relationship with the candidate; and we discovered that Iowa had its own “oops” moment — Mitt Romney didn’t actually win the Hawkeye State.

And all that was before Thursday night’s Republican primary debate in North Charleston, S.C.

View Photo Gallery: Mitt Romney, Newt Gingrich, Rick Santorum and Ron Paul take the stage for the final debate before the South Carolina primary.

Read on for our play-by-play of the CNN/Southern Republican Leadership Conference debate, the last face-off for the GOP field before Saturday’s first-in-the-South primary.

» Where and when to watch tonight’s debate
» Live discussion, analysis from The Fix
» Stakes raised for Romney ahead of tonight’s debate

10:28 p.m. | John King defends questioning Gingrich on ex-wife

As Mitt Romney might put it: No apology.

CNN’s John King says he has doesn’t regret starting off the night by questioning Newt Gingrich about the allegations of his former wife – an exchange that was among the most heated moments in tonight’s debate.

“This is one of those damned if you do, damned if you don’t (situations),” King tells CNN’s Anderson Cooper, arguing that the issue of Gingrich’s former marriage is one that Palmetto State voters are talking about.

“I knew he was going to challenge the question,” King says. “I don’t read minds. I don’t want to make a judgment about the speaker’s response. I’ve been covering politics for 25 years. I understood that if I asked the question, he was not going to be happy with it and he was going to turn on me.”

10:16 p.m. | Santorum’s closing pitch: I’m for the working class

The candidates make their closing pitches as the debate winds down, and Rick Santorum strikes a new note in his remarks.

His pitch?

“I come with the working class and strong credentials, not just with a plan, but with the character” to win in key battleground states, Santorum says.

He rattles off a list of Rust Belt states where he contends his Pennsylvania background will be an asset.

“Those are the votes and those are the states,” he says. “You want to win? Elect someone who can win in the states where we need to win.”

As the post-debate interviews kick off, Newt Gingrich tells CNN’s Anderson Cooper, “I think we can win on Saturday and if we do, it’s a whole new ballgame in Florida.”

He also says that he thinks moderator John King did a good job. And he takes aim at Mitt Romney for having more money to spend on his primary campaign.

“There is no question – Governor Romney will always have more money,” he says. “He’s the Wall Street candidate. ... He can outspend us two- or three-to-one.”

10:01 p.m. | Democrats jump on Romney’s ‘real streets’ comment

The Democratic National Committee has been quick in seizing on an exchange tonight in which Mitt Romney seeks to contrast his experience with that of Newt Gingrich. Says Romney:

“What you’ve listened to, in my view, and the speaker’s rendition of history going back to 1978 and his involvement in Washington, is, in my view, a perfect example of why we need to send to Washington someone who has not lived in Washington, but someone who’s lived in the real streets of America, working in the private sector, who’s led a business, who started a business, who helped lead the Olympics, who helped lead a state. We need to have someone outside Washington go to Washington.”

It’s the “real streets” line that Democrats have jumped on, noting that in addition to his considerable personal wealth, Romney also owns several homes.

Romney’s rivals onstage Thursday night don’t weigh in on the remark.

9:53 p.m. | Gingrich, Santorum take aim at Romney’s record on abortion

The conversation has taken a turn from taxes to immigration to the Stop Online Piracy Act (of which, unsurprisingly, the candidates are not fans) and, now, to the issue of abortion rights.

“I’m not questioned on character and integrity very often,” Mitt Romney says in response to charges by Newt Gingrich and Rick Santorum on his record. He cites aspects of his record, then adds: “You can count on me as president of the United States to pursue a policy that protects the life of the unborn, whether here in this country or overseas.”

Santorum casts himself as the most vocal anti-abortion rights candidate in the race, arguing that “what we’re talking about here is someone who’s not going to check the boxes.”

He adds that Romney should have taken pains in the Massachusetts health-care law to note that abortion services were not covered. Gingrich, too, takes aim at Romney. And the debate is about to move on to a question from Twitter, but not before the crowd weighs in.

“Ron Paul! Ron Paul!” some in the audience yell. John King turns to the Texas congressman – who’s had noticeably less time during this debate than at previous ones -- and gives him the opportunity to respond.

“But John, once again, it’s a medical subject, and I’m a doctor,” Paul says.

9:43 p.m. | Romney: ‘My dad, as you know, was born in Mexico’

Maybe Mitt Romney’s been reading “The Real Romney,” the new book by veteran Boston Globe reporters Scott Helman and Michael Kranish that delves into detail on the candidate’s life and family history.

Or maybe he’s just decided it’s time to elaborate a little more on his family’s roots while he’s on the campaign trail.

Either way, Romney is taking something of a new approach tonight in talking about his father, former Michigan governor and onetime presidential hopeful George Romney. Here’s his answer to John King when asked whether he’ll follow his father’s example in releasing his tax returns:

“My dad, as you know, born in Mexico. Poor. Didn’t get a college degree. Became head of a car company. I could’ve stayed in Detroit like him and gotten pulled up in the car company. I went off on my own. I didn’t inherit money from my parents. What I have, I earned. I work hard the American way. I’m going to be able to talk to President Obama the way no one else can that’s in this race right now, about how the free economy works.”

That’s a little bit of family history that Romney hasn’t often mentioned on the trail. A preview of things to come?

9:38 p.m. | Romney draws boos on taxes

What do we want? Mitt Romney’s taxes. When do we want them? Now.

Asked by John King when he plans to release his tax returns, Romney says that he’ll do so “when my taxes are complete for this year” – a response that wins him little love from the crowd.

“I know that if I’m the nominee, the president is going to want to insist that I show what my income was this last year,” Romney says. “So when they’re completed this year in April, I’ll release my returns in April, and probably for other years as well. ... I want to make sure that I beat President Obama, and every time we release things, drip by drip, the Democrats go out with another array of attacks.”

Ron Paul declines to be specific about when he’ll release his taxes, joking that he’d “probably be embarrassed by my financial statement” because he doesn’t have a higher income.

Newt Gingrich, who released his 2010 tax returns as tonight’s debate was getting underway, says that Romney can run his campaign as he likes but argues that sooner is better than later.

“If there’s anything in there that’s going to help us lose the election, we should know it before the nomination, and if there’s nothing in there, then why not release them?” Gingrich says. “I mean, it’s a very simple model.”

And Rick Santorum?

“Well, I do my own taxes, and they’re on my computer and I’m not home. So, I have nobody at home right now. Until I get home, I won’t get them. When I get home, you’ll get my taxes,” he says.

But it’s Romney’s answer that seems to draw the greatest displeasure from the crowd – at one point, he even gets boos for this statement:

“As has been done in the past, if I’m the nominee, I’ll put things out at one time so we have one discussion of all of this,” he says. “I obviously pay all full taxes. I’m honest in my dealings with people. People understand that. My taxes are carefully managed.”

He goes on to defend himself by noting that “I pay a lot of taxes. I’ve been very successful. And when I have our taxes ready for this year, I’ll release them.”

9:14 p.m. | Tweets, pictures from S.C.

9:10 p.m. | ‘Grandiosity has never been a problem with Newt Gingrich’

Things are getting personal between Rick Santorum and Newt Gingrich.

The former senator and former speaker – who served together in the House for four years, from 1991 to 1995 – are doing battle over Gingrich’s tenure leading the lower chamber.

“Grandiosity has never been a problem with Newt Gingrich,” Santorum says, taking aim at Gingrich’s reputation for big ideas. Taking a page out of the Romney campaign playbook, Santorum casts Gingrich as an unpredictable leader.

“I don’t want a nominee that I have to worry about what he’s going to say next, and that’s what I think we’re seeing here,” Santorum says. To Gingrich’s suggestion that Santorum should drop out of the race and endorse him, the former senator responds: “These are not cogent thoughts, let’s just be honest.”

“Newt’s a friend; I love him,” Santorum continues. “But at times, you’ve just got that sort of worrisome moment, that something’s going to pop. And we can’t afford that in a nominee. I’m not the most flamboyant, and I don’t get the biggest applause lines here. But I’m steady. I’m solid. I’m not going to do things that you’re going to worry about. I’m going to go out there and make Barack Obama the issue in this campaign.”

Gingrich turns the tables on Santorum’s “grandiosity” argument, contending that “it’s a very simple question: how big a scale of change do we want in Washington?”

“You’re right. I think grandiose thoughts. This is a grandiose country. ... And we need leadership prepared to take on big projects,” he says to applause.

Before the conversation moves on to taxes, things get even more personal.

“I served with him,” Santorum says of Gingrich. “I was there. I knew what the problems were going on in the House of Representatives when Newt Gingrich was leading it. It was an idea a minute. No discipline.”

8:56 p.m. | Santorum takes aim at Romneycare

It’s Romneycare time.

After a series of debates in which Mitt Romney’s rivals seemed to give him a pass on the Massachusetts health-care law he helped implement, the GOP field tonight is out for blood.

“Governor Romney tells a very nice story about what his plan is now,” Rick Santorum says. “It wasn’t his plan when he was in a position to do a plan.”

He blasts Romney for what he calls “a government-run health-care system that was the basis of Obamacare.”

“It’s abject failure and he has stood by it,” Santorum says, arguing that both Romney and Newt Gingrich have been “playing footsie with the left” on health care.

Romney responds by contending that, by implementing the health care law, he was “showing compassion for people who don’t have insurance.” He also restates the argument that he has made before that decisions on health care are best left up to the states.

“My view is, get the federal government out of Medicaid,” Romney says. “Get out of health care. Return it to the states. And if you want to go be governor of Massachusetts, fine. But I want to be president and let states take responsibility for their plans.”

His defense gets a round of applause from the crowd.

Gingrich, meanwhile, returns fire at Santorum, calling the former senator’s criticism of his record on health care “mildly amazing.”

“I can say, ‘I was wrong and I figured it out. You were wrong and you didn’t,’” Gingrich says in response to Santorum’s criticism. The audience greets him with cheers.

“You held that position for over 10 years,” Santorum responds. “And it’s not going to be the most attractive thing to go out there and say, ‘You know, it took me 10, 12 years to figure it was wrong, when guys like Rick Santorum knew it was wrong from the beginning.’”

John King turns to Ron Paul and asks him to weigh in on the issue.

In a jab at his lack of debate time thus far, Paul deadpans: “I thought you were prejudiced about doctors or against doctors who practiced in the military or something.”

8:33 p.m. | A defiant Gingrich responds to ‘open marriage’ statement by ex-wife

John King cuts right to the chase and directs his first question to Newt Gingrich, asking the former House speaker about his former wife’s statement to The Washington Post and in a forthcoming ABC News interview that Gingrich had wanted “an open marriage.”

“Would you like to take some time to respond to that?” King asks.

“No. But I will,” says a defiant Gingrich, to a burst of applause from the crowd.

“I think the destructive, vicious negative nature of much of the news media makes it harder to govern this country, harder to attract decent people to run for public office, and I am appalled that you would begin a presidential debate on a topic like that,” Gingrich says, to an extended round of cheers.

Gingrich continues, taking his time as he responds: “Every person in here knows personal pain. Every person in here has had someone close to them go through painful things. 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 that I can imagine.”

“And I am frankly astounded that CNN would take trash like that and use it to open a presidential debate,” he adds.

King responds by pointing out that the network that is airing the interview with Marianne Gingrich is ABC, not CNN, but also notes that “it is a subject of conversation in the campaign.” The crowd begins to boo.

“John, John, it was repeated by your network, you chose to start the debate with it,” Gingrich says. “Don’t try to blame anybody else. You and your staff chose to start this debate with it.”

Gingrich’s response represents something of a gamble – but it’s also in keeping with his strategy in nearly every primary debate thus far of taking aim at the mainstream media.

Will it pay off?

Rick Santorum weighs in, saying that “this country is a very forgiving country” but that candidates’ personal and public lives should be examined.

Mitt Romney, for his part, declines to press the issue when given the chance by King.

“John, let’s get on to the real issues, that’s all I’ve got to say,” he says.

8:20 p.m. | Santorum: ‘A most welcome victory’ in Iowa

Rick Santorum takes the opportunity right off the bat to thank Iowa for his belated victory there.

“I want to thank the people of Iowa for a little delayed but a most welcome victory there,” Santorum says to cheers from the crowd.

Both he and Mitt Romney in their opening remarks make note of their families – something that Newt Gingrich does not do. Instead the former speaker makes note of his Southern roots.

“It feels good to be back at home in the South, and I look forward to this evening,” Gingrich says.

For his part, Ron Paul begins his introduction by reminding the crowd, “I am a congressman from Texas.”

8:13 p.m. | And we’re off

Our debate has kicked off.

Moderating tonight from the North Charleston Coliseum is CNN’s John King. The four contenders: Former Massachusetts governor Mitt Romney, former House speaker Newt Gingrich, Rep. Ron Paul (Texas) and former senator Rick Santorum.

8:0 p.m. | How well do you know the candidates?

Which GOP hopeful was once a registered Democrat? Who has the fewest total years in elective office? Which candidate has a Ph.D.?

Try your hand at our GOP candidate match game and test your knowledge of the Republican presidential field.

7:48 p.m. | Jenny Sanford: Gingrich wouldn’t get my vote

Herman Cain has spoken. Sarah Palin has made her pick. And now, Jenny Sanford has weighed in on the South Carolina primary.

Sanford, the former wife of onetime South Carolina governor Mark Sanford (R), told MSNBC’s Chris Matthews Thursday night that she would not back former House speaker Newt Gingrich (R-Ga.) in the Palmetto State’s nominating contest.

“As a voter, I encourage people to look at both sides, the personal side,” Jenny Sanford said on “Hardball.” “And if you’re going to overcome somebody’s moral failings or infidelities, you have to also look at where they stand ideologically and how much does their rhetoric match their reality. In my mind, Gingrich falls short on both fronts. So, he wouldn’t get my vote.”

Sanford – who divorced Mark Sanford in 2010 after the former governor revealed he was having an affair with Maria Belen Chapur, a woman in Argentina -- was responding to the news earlier Thursday that Gingrich’s second wife, Marianne, is going public with the private details of her 18-year marriage to Gingrich.

Among Marianne Gingrich’s revelations is her charge that Gingrich wanted “an open marriage” — an allegation to which the candidate has declined to respond.