Rick Santorum gave his best performance and Newt Gingrich blasted CNN Thursday night at the news station's Republican presidential debate in Charleston, South Carolina.

The event, moderated by John King, concluded a dramatic news cycle that included Texas governor Rick Perry quitting the race and Newt Gingrich's ex-wife emerging from the shadows with an unflattering ABC interview.

The stakes were certainly high by the time 8 p.m. rolled around, as the debate is last real chance Santorum, Gingrich, Romney and Ron Paul had to woo South Carolina voters ahead of the state's critical primary this Saturday. If Romney wins over the weekend, he'll likely coast through the rest of the season to the Republican nomination.

Romney, however, did not coast through tonight's debate. Gingrich exploded at King for opening the debate with questions about his ex-wife, Santorum stepped up to the plate and Paul desperately tried to squeeze in answers (with the help of the audience). How did the four candidates measure up?

Rick Santorum Strikes Back

Santorum understood this was the night to either make it or break it. Romney and Gingrich were both leading in the South Carolina polls and the former Pennsylvania governor's would probably not last more than a few weeks if he didn't have a strong showing in the state's primary. Santorum delivered; he wasn't afraid to hit his biggest rivals where it hurt.

Perhaps he was boosted by the Iowa caucus recount that revealed he actually led Romney by 34 votes, but Santorum attacked Romney with confidence. After Romney went through his regular schpeal of defending his Massachusetts health care legislation - the one GOP opponents say inspired the much dreaded Obamacare - Santorum engaged him and wouldn't let him go. He's standing by (Romneycare) and he's going to go up against the president, Santorum said.

While he avoided criticizing Gingrich's personal life, Santorum used sound bite after sound bite to attack the former Speaker's rocky end in the house and explosive personality. He called Gingrich grandiose and better at thinking up ideas rather than acting them. If Newt's the nominee, he said, he worries something's going to pop. He reminded everyone how Newt Gingrich's speakership ended with a coup (Gingrich preferred to call himself a principled rebel). And it was a smart move for Santorum, a candidate largely defined by his social conservatism, to not take John King's bait and attack Gingrich on his marriages or ex-wife's campaign to ruin him.

It was around this moment when Politico's Maggie Haberman tweeted an insightful comment. Oh. My. God., she wrote. Santorum is doing what Perry never did.

In fact Santorum did the very opposite of what the Texas governor did. While he lagged behind in the race, he used the stage to hound the candidates on their weaknesses. Perry's inability to do that transformed him quickly from surging Romney alternative to campaign dropout. But we'll have to wait until Saturday to see if it makes any difference.

Newt Gingrich Goes Nuclear on CNN

The usually captivating candidate had his most animated moments in the first five minutes of the event. King kicked things off by bringing up the much-anticipated ABC interview with his ex-wife, who appears to determined to ruin his shots at the presidency. Gingrich had spent the morning dismissing the interview, which included Marianne Gingrich's claim that the GOP hopeful demanded an open marriage.

When it comes to his controversial personal life, Newt has found his war on the media is the best go-to strategy.

I am appalled that you would begin a presidential debate on a topic like that. he said to a standing ovation, and boos at King.

I am frankly astounded that CNN would take trash like that and use it to open a presidential debate. He concluded, The story is false, and directed more anger toward the media, accusing them of trying to get Obama re-elected. The audience roared even more with applause.

Where his rivals were concerned, Gingrich spent most of the debate defending himself. But he did have some memorable zingers against Obama.

I'd love to do a three-hour Lincoln-Douglas debate with Obama, he said. He can use the teleprompter. I'll just rely on my knowledge.

Mitt Romney Is from the streets of America

As more podiums are removed and the stage gets smaller, Romney comes under more scrutiny. Thursday night, the front-runner floundered.

At the beginning, the former Massachusetts governor went to his dependable, go-to strategy of bringing everything back to Obama. When asked about job creation while CEO of Bain, he changed the topic to Obama. He said he'd like to stuff economy down Obama's throat in the general election. At the end of the debate, when asked what he have done differently in his campaign, he said, I wish I took all the time I spent talking about one of these guys on stage and spent it talking about Obama.

But that was precisely Romney's problem. Unlike Santorum or Gingrich, Romney isn't very natural in a debate; instead of engaging the candidates, he recites a well-rehearsed speech. He came across as fake when he tried to relate to Americans. In one of his few attacks on Newt, the best he could do was a cheap Reagan reference. You're only mentioned once in the Reagan diary, he said.

Romney also had a shaky response about releasing his taxes. When CNN's King asked him if he'd follow his father's example and release his tax forms every year, he said maybe and kind of chuckled. That was met with jeers. It was weird when he said, I've lived in the real streets of America. He stammered when asked about his flip-flopping stance on abortion, saying now isn't the time to doubt people's words.

But at the end of the response to King's tax question, he finally got it together. I'm not going to apologize for being successful, he said. I made my money the American way. That got cheers, and should have been Romney tone from the beginning.

Romney still had a few colorful moments. When asked what he would change about his campaign if he could, he would try to get 25 more votes in Iowa. That got laughs.

Ron Paul, Sidelined

Ron Paul was in this debate, remember? As things escalated to a punching match between Romney, Gingrich and Santorum, the Texan struggled to make his presence known.

There was even one point when the audience screamed at John King because he passed over Paul for a question about abortion. Remember, I'm a doctor, he said, urging King to let him speak on the issue. In fact, Paul continued to remind the audience that he was a veteran and a gynecologist in the military throughout the debate.

When he did speak, Paul's military shout-outs were probably a smart thing for him to do. Veterans are one of his strongest bases and among his biggest donors.

Foreign policy, however, isn't the candidate's strong suit. Most conservatives are turned off by Paul because he is against most foreign aid and pursuing terrorists abroad - which earned him boos at the South Carolina debate Tuesday. But John King didn't bring up global issues at all.

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