If there's ever been a presidential debate with as much news happening in the hours leading up to the event, it's hard to remember when.
In just a few hours' time, we've learned that Texas Gov. Rick Perry dropped out of the race and endorsed Newt Gingrich; that Rick Santorum may actually have won the Iowa caucuses; that Gingrich's second wife alleged he demanded an open marriage so she could share him with Callista, wife No. 3, and that the same Gingrich was apparently closing the gap in polls in South Carolina and nationally.
That would be a lot to digest in a week, and yet it all happened within hours of the debate in Charleston, S.C., to be shown by CNN starting at 8 p.m. EST Thursday. The debate is sponsored by the Southern Republican Leadership Conference, among others.
Perry's departure leaves just four candidates on the debate stage, Mitt Romney, Gingrich, Santorum and Rep. Ron Paul of Texas. That's both good and bad news for the candidates.
It's certainly a positive in that it gives each of them more time to deliver their by now well-honed campaign themes and to throw rhetorical darts at their rivals.
The dart-throwing part also explains why it's bad. There will be more time for each candidate to squirm by questions put to him by either his rivals or the journalists serving as inquisitors.
Here's just some of what the candidates will have to contend with in a debate that has the potential to produce some real political fireworks because of all the news beforehand, the reduced number of participants and the fact that it's the final debate before what's widely viewed as the most significant test yet of the Republican candidates in the 2012 presidential cycle.
Romney — The former Massachusetts governor is sure to be asked about the 15 percent tax rate he has admitted to paying on much of his income. A likely question: How does he explain the fairness of a system in which he pays a 15 percent federal rate as a superwealthy investor with assets estimated at $250 million while a middle-income plumber pays upwards of twice Romney's rate?
Romney also will no doubt be asked about the ABC News report that he has parked some of his wealth in offshore accounts in the Cayman Islands, a tactic that has long been used by the rich hoping to avoid taxes.
Speaking of taxes, Romney is also sure to be pressed on releasing his tax returns. With one of his most important political allies, New Jersey Gov. Chris Christie, saying he should release them sooner rather later, the pressure is mounting on Romney to release them before April, when he suggests he might do so, and to release his returns for 10 years or more.
Romney is also likely to be asked about his apparent loss in the Iowa caucuses that officially had been, until Thursday, a narrow, eight-vote win. It turns out that he didn't make history after all, because he didn't win in both Iowa — where he wasn't expected to — and New Hampshire, where he was. Was it a mistake for him to make too much of Iowa when the race was so close to begin with?
Romney has an interesting choice to make in terms of how he deals with his rivals. In many debates, he has acted like the eventual GOP nominee, aiming his attacks mainly at President Obama.
Does he continue that tack tonight? Or does he try to damage both Gingrich, who has been gaining in the polls, and Santorum, who has gotten the support of national evangelical Christian leaders?
Gingrich — Where do we start? Gingrich is sure to be questioned about the accusation from his second wife, Marianne Gingrich, that in 1999 he asked her for an open marriage so he could keep her and his extramarital inamorata, now third wife, Callista, in his life.
How does that comport with a candidate who professes to be pro-family, he will very likely be asked, or some variation of that.
There are two Gingriches who could answer that question. The first is the vinegary, condescending, self-righteous one who would use the opportunity afforded by that question to engage in media bashing. That Gingrich isn't attractive to independent voters, though he does appeal to raw-meat conservatives.
The second Gingrich is the contrite one who has sometimes explained that he has asked his Maker for forgiveness and is now a grandfather and a better man.
Since Gingrich's problem is making voters see him as being presidential timber, the second Gingrich might be the better choice in terms of swaying those voters who have their doubts.
Thursday night will be Gingrich's last chance, at least on a debate stage, to pull down Romney before the South Carolina primary Saturday. So it would be a surprise if he pulled his punches and didn't go after Romney once again on his days at Bain Capital.
Santorum -- The former U.S. senator from Pennsylvania was fairly feisty at Monday night's debate, and that was before Iowa officials said he had actually received 34 more votes than Romney in the caucuses.
The delayed announcement should have Santorum leaning aggressively forward even more as he attempts to rattle Romney and demonstrate why he and not Romney or Gingrich is the true conservative choice in the race.
Santorum has a problem not unlike Gingrich's, however. No, not the open-marriage thing but the presidential thing. He'll be standing onstage with Romney, who, many voters say — despite all their doubts about him — looks like a president.
Can Santorum do anything tonight to make himself appear more presidential? That remains one of his biggest challenges.
Paul — The Texas congressman has perhaps the most loyal base of supporters of any of the remaining Republican presidential candidates.
But the debates have showcased some of his views on national security and foreign policy that are clearly out of step with Republican Party orthodoxy. That makes it no easy task to come up with a scenario whereby he would become his party's nominee.
Still, Paul can be a factor in Thursday night's debate by highlighting the weaknesses from a conservative perspective of each of his remaining candidates as he has in earlier debates and in TV ads.
Because Paul's supporters are so loyal and are quick to take exception to real or perceived slights of their candidate, it presents his rivals with a dilemma. Do they counterattack against his attacks on them and possibly alienate his supporters? Or do they just frown and change the subject as soon as they have the chance to?