The second South Carolina debate is tonight, and the 2012 Republican primary race is heating up. Mitt Romney and Newt Gingrich are battling for the top spots in the Southern state, with Ron Paul and Rick Santorum behind.

But just as the candidates were preparing for their final debate before Saturday's primary, a series of bombshells, sudden endorsements and uncomfortable revelations were thrown into the mix. From Rick Perry withdrawing to Marianne Gingrich's hotly anticipated interview with ABC tonight, here are five ways the GOP race changed today.

1. Rick Perry Drops Out 

Just as Jon Huntsman dropped out after a poor third place in New Hampshire, the Texas governor has announced his decision to withdraw from the Republican primaries just before the second South Carolina debate tonight.

As a Texan, I've never shied away from a fight, Perry said. [But] I know when it's time to make a strategic retreat.

Perry had been polling in the single digits when he gave another lackluster debate performance in Myrtle Beach on Monday.

But his decision to drop out triggered an endorsement of Gingrich, and opens the way for the former speaker and Santorum to fight it out as the ultimate anti-Romney, with Paul cornering the libertarian vote.

I know we can't lose track of the ultimate objective in carrying out our mission, and that objective is not only to defeat President Obama, but to replace him with a conservative leader who will bring about real change, Perry said in a dig at Romney's moderate record.

At the moment, Gingrich is closing the gap with Romney in the latest polls, even topping the former Massachusetts governor in  Public Policy Poll and Rasmussen surveys.

Now that Gingrich is asking Perry supporters to turn their candidate's endorsement into a vote, the former House speaker is poised to pose a serious threat for the nomination.

2. Marianne Gingrich Promises Bombshell in ABC Interview

Of course, Perry's endorsement came on the same day that ABC announced that Marianne Gingrich, the candidate's second wife, would be giving an exclusive interview immediately after the debate. What clips have been leaked point to a picture of Gingrich that is very unflattering.

In a 30-second teaser, Marianne Gingrich claims her husband made a habit of being in bed with current third wife Callista after every speech... but would call still Marianne to tell her he loved her after he'd slept with his mistress.

When Marianne confronted Gingrich about the affair, she claims he demanded that she share him with Callista, essentially asking for an open marriage.

And in an interview she gave to Esquire back in 2010, Marianne Gingrich spilled dirt not only on her ex-husband's personal life, but his professional one as well.

He believes that what he says in public and how he lives don't have to be connected, she scoffed when asked about his chance of being elected. If you believe that, then yeah, you can run for president.

She even claims that when Gingrich's career had its first downward spiral, back in 1997, his staff had to resort to gallows humor to deal with his increasingly manic behavior, saying: He's a sociopath, but he's our sociopath.

3. Jon Huntsman's Daughters Undermine Romney Endorsement

ABC leaked a video today that Jon Huntsman's daughters had opted not to post on their public YouTube account. Why not? Because unlike their video mocking Herman Cain, here the Huntsman trio chooses to go after cornball candidate Romney, and to slam fake news network Fox.

Most of the video centers on a fake interview between the three Fox hosts (all wearing blonde wigs) and a bobble-head doll standing in for the former Massachusetts governor.

Though the video is obviously meant in fun, watching the three girls relentlessly mock Romney (Would you be able to defend yourself against, say, a honey badger? one asks halfway through) may end up denting the impact of their dad's endorsement for Romney earlier this week.

The Huntsman daughters, however, aren't getting much flak for their video. In fact, the sassy attitude of Huntsman's daughters so impressed the Boston Herald that the paper has asked the girls to stay in the campaign, even with their father no longer running.

Watch the video below:

4. Rick Santorum Won the Iowa Caucuses by 34 Votes

Iowa Republican officials report that Santorum, initially reported to be eight votes behind Romney in the Jan. 3I caucuses, actually has a 34-vote lead.

According to the Des Moines Register, however, Santorum cannot declare himself the winner even with this recent surge, since the results from no less than eight precincts are still missing and need to be verified.

But even if the GOP is calling Iowa a split decision, Santorum still goes into the second South Carolina debate with some serious bragging rights, turning an unusual near tie into a completely unexpected (if unofficial) win.

After a poor showing in New Hampshire, this recent boost could give Santorum a leg up in the South Carolina polls, an advantage that he desperately needs.

5. Mitt Romney's Tax Returns Become Pre-Debate Hot Topic

Matt Romney may have been able to distract voters briefly from his father's financial records by cracking a birther joke, but as of Thursday, the pressure is on for Mitt Romney to release his tax returns.

Perry led the reinvigorated scrutiny into Romney's records when he called on the former Bain capital CEO to be honest with American citizens.

And only one day later, Romney himself told reporters (in a move apparently not coordinated with his campaign) that his tax rate was around 15 percent, a substantially lower number than average middle class families are forced to pay, let alone multi-millionaires.

For the past 48 hours, both Democrats and Romney's Republican rivals have been shouting that 15 percent figure for everyone to hear, and even some of his supporters admit that the candidate mishandled his revelation.

To add on to the message that Romney is a one percenter, ABC News is now reporting that the former Massachusetts governor is keeping millions of dollars stashed in the Cayman Islands, a notorious tax haven, and that he donated thousands of Bain Capital shares to the Church of Jesus Christ of Latter-day Saints in a charity writeoff.

There's no question that Romney's tax returns will come up in tonight's South Carolina debate. The question is whether his campaign can seize back control of the message enough to keep the candidate's revelations from losing him the primary state.