Polls close at 7 p.m. ET. If PPP and ARG are right, the race should be called at around 7:01. But maybe they’re not right: More than 22,000 absentee ballots were cast, many of them before Newt’s last-minute surge, so Romney might be stronger than he seems. On the other hand, reporters are chattering about Democrats in South Carolina voting for Newt in order to prolong the Romney/Gingrich war. Read pollster Mark Blumenthal on why trying to predict a race with lots of eleventh-hour developments is a fool’s errand.

Here’s Google’s page for South Carolina election returns. Assuming Newt wins, the margin obviously matters in shaping the pre-Florida spin. If it’s narrow, Romney will claim that Gingrich won only because SC is in his backyard. If it’s wide, you’ll hear the phrase “aura of inevitability shattered” roughly eight thousand times over the next few days. See Ed’s post this morning on why Romney probably isn’t worried, even if he ends up swamped tonight. He’s piling up absentee ballots in Florida, where he currently holds a huge lead, and rumors continue to fly about him rolling out Jeb Bush for the big endorsement at an opportune moment. And then there’s this:

After Florida, Gingrich’s outlook becomes even more bleak. The February calendar presents Romney with the opportunity to do to Gingrich what Barack Obama did to Hillary Clinton in 2008. Caucuses in Nevada, Colorado, and Minnesota will benefit a more organized campaign, giving Romney and Rep. Ron Paul a boost over Gingrich. The two primaries that month, in Arizona and Michigan, will take place on Romney-friendly turf; Arizona has a sizable Mormon electorate, while Michigan is Romney’s home state. By the end of February, Romney is likely to have the majority of the 274 delegates awarded to that point. Paul’s focus on caucus states means Gingrich may not even be in second place by the end of the month.

Then comes Super Tuesday, when 10 states will allocate a total of 407 delegates. With few debates left on the horizon, Gingrich won’t have the time, the exposure, or the money to build the type of national campaign Romney has already started to build (Gingrich isn’t even eligible for the 46 delegates from Virginia; his campaign didn’t submit enough valid signatures to make the ballot there).

In short, South Carolina presents Gingrich’s last real chance to be on equal footing with Romney before the race goes national. Barring a sustained surge in campaign contributions for Gingrich and a real stumble by Romney’s campaign, the reality is that the race for the Republican nod is as clear today as it was before Gingrich’s revitalization: There will be no extended fight for delegates a la Obama-Clinton, there will be no brokered convention, and Romney will be the Republican nominee. The deck is stacked too much in Romney’s favor to give Gingrich’s campaign anything more than a temporary reprieve.

Once Gingrich is formally crowned Not Romney tonight and becomes the last real obstacle to Mitt’s nomination, he shouldn’t have any trouble raising money for months to come. One of his advisors told Stephen Hayes, in fact, that Newt will be in it until the convention. I wouldn’t rule out a “real stumble” from Romney on the trail either. As effective as Gingrich has been this week, Romney has been terrible, hemming and hawing about his tax returns to feed the suspicion that he has something to hide and letting his campaign stupidly float the idea that he might back out of one of the Florida debates, which plays right into Newt’s message that he isn’t tough enough to handle Obama. He won’t implode in a flash the way Perry did with his answer on in-state tuition for illegals, but if he continues to look weak and untrustworthy he could bleed enough support to keep Gingrich going.

Here’s your thread to follow results; lots of updates to come, including a link to the exit polls as soon as they’re available. Ed will be on Hugh Hewitt’s show sometime between 7 and 9 p.m. ET to talk about the results, so be sure to tune into that too.

Update: The hard feelings begin before the vote ends:

Not to be outdone, Romney’s campaign later put out a statement celebrating the “15th anniversary” of the House decision to reprimand Gingrich for ethics violations, during his days as speaker. The Romney campaign plans to deliver an anniversary cake to Gingrich’s South Carolina headquarters to mark the occasion on Saturday.

Update: Behold, my friends, as Team Romney prepares the ultimate “You know who this benefits?” spin:

“I think we’re going to lose tonight, we could lose big,” the aide said, speaking on condition of anonymity. “But I think it’s been a terrible week for Gingrich and a great week for us.”

From the former Speaker’s demonization of Romney’s business record, to his decision to indignantly deflect criticism from his ex-wife, the aide said Gingrich has ensured that he won’t win the Republican nomination…

Of course, a loss is still a loss, and up until very recently, Romney and his surrogates had been predicting a first-place finish in the Palmetto State. Asked whether Romney’s collapse in the polls is forcing Romney’s campaign to consult its own mortality, the aide laughed.

“Oh God, no,” he said. “I mean, to face Newt Gingrich?”

Update: Here comes the exit poll data. You know who this doesn’t benefit?

Sixty-four percent said the debates were an important factor for them; just 34 percent said they were not. Gingrich won standing ovations in both debates while Romney often struggled – and at one point received a smattering of boos for equivocating over how many years of his tax returns he would release.

Gingrich, who polls suggest overtook Romney in the final days before today’s primary, is hoping for a victory that would keep Romney from locking up the nomination before the end of the month. A majority of voters – 53 percent – said they made up their mind about who to back within the last few days.

Forty-five percent say electability is most important. We’ll see how that breaks between Gingrich and Romney.

Update: Looks like it’ll be a short night: “Romney aides tell Fox News they expect a second place finish based on exit polls.”

Update: Nate Silver sends a chill through Team Romney by wondering whether he’s still ahead … in Florida:

Essentially all of the polling data used for the forecast, however, predates the Monday night debate in Myrtle Beach, since which time there has been a dramatic reversal of fortunes in the Republican race. Mr. Romney has lost 15 points from his lead nationwide, according to the Gallup national tracking poll. There has been an even larger swing – a net of about 21 points between Mr. Romney and Mr. Gingrich – in South Carolina.

If the Florida polls have swung as much as the national polls during the past several days, Mr. Romney would have only about a 5-point lead there now. And if the Florida polls have swung as much as the South Carolina ones have during the last week, Mr. Gingrich and Mr. Romney would now be essentially tied there.

The wider the margin tonight, the more buzz Newt will have and, presumably, the more momentum heading into Florida. (There’s another debate on Monday too, don’t forget.) Speaking of which, here’s the answer to the electability question I posed above about the exit poll data: Of the 45 percent who said beating Obama was most important, 49 percent said Gingrich was best positioned to do it compared to just 41 percent who said Romney. In South Carolina, Newt’s the electable candidate.

Update: A picture is worth a thousand words.

Update: All the nets are calling it for Gingrich promptly at 7 p.m. Stand by for exit poll data so that we’ll have some sense of the margin.

Update: Here’s the exit poll data. Newt wins, 38/29.

Update: The most amazing thing about the exit poll is how many different demographics Newt won. Romney led by double digits less than a week ago but couldn’t hold onto his advantage in virtually any group. Newt won men, women (sorry, Marianne), independents, marrieds, singles, veterans, non-veterans, and all income groups. He won on electability and on the economy and on the deficit. He won among voters who decided today and within the last few days, and tied Romney among those who decided earlier this month. (A rare win for Romney came among those who decided before that.) He even won among those who approve of Nikki Haley’s job performance as governor, notwithstanding her endorsement of Mitt.

As for Bain, here was the response when voters were asked their view of Romney’s background of investing in and restructuring companies:

Most think positively of Romney’s career, but Mitt beats Newt within that group fairly narrowly. Among the minority who view Romney’s career negatively, Gingrich crushes Romney. Could be that the Bain attacks didn’t matter much to most voters, but to the voters who cared, they mattered a lot.

Even though Newt topped Mitt on nearly all the issues, I think this’ll be the media spin tomorrow: “Romney lost on the basis of two debates. Welcome to U.S. of American Idol”.

Update: For what it’s worth, here’s the Democratic reaction tonight via our old friend KP: “Getting ecstatic emails from my Dem operative friends re Newt.”

Update: A mind-boggling exit poll data point from John Dickerson. I guess that ABC interview with Newt’s ex didn’t work: “Gingrich got the same share of the evangelical vote in SC as Mike Huckabee in 2008. One of them is an ordained minister.”

Update: Two more tidbits from the exit poll. In case there was any doubt, yes, Gingrich killed Romney at the debates:

As for this, make of it what you will:

Update: One more and then I’ll stop. This doesn’t prove that the Bain attacks worked, but I’m not sure that’s a comfort to Mitt. If voters are starting to feel alienated by Romney’s wealth, whether because they think he doesn’t understand their problems or for other reasons, then Gingrich could become the “blue-collar candidate” by default and suddenly Mitt has a big problem:

Update: Team Mitt would have preferred to roll out the Jeb Bush endorsement closer to the Florida vote, but I guess they’re panicky about a “sinking Romney ship” narrative tomorrow. Three sources are telling CNN tonight that Jeb will in fact endorse Mitt sometime soon. Will that be enough, though, if Santorum drops out? Says PPP, “Florida Santorum voters prefer Newt over Mitt 58-32…his decision whether to stay in or not will have major implications”.

Update: Chris Cillizza of WaPo tweets that “Close Jeb Bush ally tells me that no Romney endorsement is in the works.” Jeb’s camp being coy, or is he getting cold feet about throwing in with Romney after tonight’s drubbing?

Update: Santorum’s speaking as I write this and Ed notes on Twitter that he’s using the past tense a lot. Him dropping out would be Romney’s worst nightmare, needless to say.

Update: Wouldn’t you know it, Nikki Haley couldn’t make it over to the Romney rally tonight. Sad.

Update: Here’s Mitt’s concession speech. The money line: “Our party cannot be led to victory by someone who also has never run a business, and never run a state… We cannot defeat [Obama] with a candidate who has joined in that very assault on free enterprise.”

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Update: At long last, more than three hours after the race was called for him, here’s Newt. Quote: “I articulate the deepest-felt values of the American people.”

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Update: Oh my. Did Jeb just head for the lifeboats on the S.S. Romney?

Jeb Bush, the popular former Florida governor, said he will “stay neutral” in the Republican presidential primary while warning his party’s candidates to leave the “circular firing squad” of their primary debates behind and start appealing to a broader audience of voters.

Bush’s remarks, in an exclusive interview today, come as the contest advances to Florida, where the Jan. 31 primary will take the race into its biggest and most diverse arena yet. The winner will be awarded all of the state’s 57 delegates…

The younger Bush described both Romney and Gingrich as “credible” candidates in a November contest with President Barack Obama. “I intend to help whoever wins the nomination,” the former governor said…

He also says Romney should disclose his income tax records during the Florida contest, calling Romney’s riches “a wonderful success story.”

Bush is going to spin this as having been his position all along but the rumors that he’d endorse Mitt have been circulating for weeks. (His dad endorsed Romney a few weeks ago, remember.) The fact that he’s declaring neutrality on the same night that Gingrich swamped Romney in South Carolina is a terrible signal for Mitt.