First Read points out Mitt Romney’s fundamental problem: “He’s been unable so far to win over conservatives in a conservative state. And if he’s unable to beat Gingrich and Rick Santorum in South Carolina — both of whom have their shortcomings — it would send a flashing warning signal to party leaders. What’s more, it would produce chatter, fair or not, that the party needs to find someone else, just as Indiana Gov. Mitch Daniels is set to deliver the GOP response to President Obama’s State of the Union on Tuesday night.”

“And chew on this: Did Team Romney make a mistake by playing so hard in South Carolina? As soon as his campaign gladly accepted Gov. Nikki Haley’s endorsement, it raised the stakes of a contest that was never going to be easy for him.”

Nate Silver: “I had written a post on Tuesday that challenged the
notion that there was a true ‘anybody but Romney’ constituency among
Republican voters… But now I’m wondering if that is the right
interpretation. Mr. Gingrich’s gain in the polls has occurred so rapidly
that few political writers have taken a step back to analyze it. What’s
interesting, however, is that in each of the first three voting states,
there is a different “not Romney” candidate who has surged late in the
race: Mr. Santorum in Iowa, Jon M. Huntsman Jr. in New Hampshire, and
now Mr. Gingrich in South Carolina… Where I think things become
potentially dangerous for Mr. Romney is when he plays into this tendency
by playing prevent defense, and behaving as though the nomination is
his to lose… Our forecasts now say that Mr. Gingrich has become the
slight favorite to win in South Carolina. We will see whether that comes
to fruition, but Mr. Romney’s prevent defense has allowed Mr. Gingrich
to drive to his 30-yard line.”

Mitt Romney said at last night’s debate “he’ll release his tax returns in April — but the booing that drew suggests Republican primary voters don’t appear willing to wait,” Politico reports.

“The tax returns delay provides the opening for growing suspicion and unease about the candidate who’s been leading the polls here.”

Jonathan Cohn: “What is in Mitt Romney’s tax returns? I have no idea, but I’m starting to wonder if it’s even more damning than speculation has suggested. Romney’s answers on the tax questions were rambling and unclear, which is remarkable for a candidate who is so intellectually sharp, who prides himself on careful preparation, and who had to know the question was coming. This issue has rattled him, obviously, and I’m eager to find out why.”

Dave Weigel: “The tax return question was totally predictable, and Mitt Romney blew it.”

Andrew Sullivan: “Romney then completely flounders in response to John King’s brilliant citation of George Romney’s position on the matter. And that word — ‘maybe’ — in answer to a direct and simple question is devastating.It not only makes him look shifty; it makes him look as if he doesn’t respect his own father’s honorable example.”

Walter Shapiro: “Thursday night’s four-top GOP debate made it official: The South Carolina primary has become a referendum on Newt Gingrich. Just 10 days after he was left in a dustbin labeled ‘Yesterday’s Man’ after dismal finishes in Iowa and New Hampshire, Gingrich has confounded the experts yet again. The oft-derided and consistently under-estimated House speaker has now bested Jesus in his sheer number of resurrections — an association that can only help as the South Carolina primary vote looms.”

A new We Ask America poll in South Carolina shows Newt Gingrich leading the GOP field with 32%, followed by Mitt Romney at 28%, Ron Paul at 13%, Rick Santorum at 9%, Rick Perry at 3% and Jon Huntsman at 3%.

A new  Public Policy Polling survey also show Gingrich continues to lead Romney, 35-29, with Paul and Santorum each tied for third at 15%.

Nate Silver: “Our forecasts now say
that Mr. Gingrich has become the slight favorite to win in South
Carolina.”

“No, but I will.”

— Newt Gingrich, when asked in last night’s Republican presidential debate whether he would like to respond to
reports that he requested an “open marriage” with his ex-wife. Those
words began a five minute attack on the media which Alex Roarty calls “one of the most memorable moments in debate history.”

Elizabeth Warren, the likely Democratic challenger to Sen. Scott Brown
(R-MA), raised over $1 million in just 24 hours during their first
“money bomb” of the election, The Hotline reports.

Not so fast:
“There aren’t many candidates who can muster that kind of support in a
money bomb. One of them, though, is Warren’s opponent: Almost exactly
two years ago, when Republicans started to think they had a real shot at
winning the seat, Sen. Scott Brown raised more than $1 million a day,
three days in a row.”

With Rick Perry now out of the race, the four candidates remaining on the stage tonight had a chance to really engage with one another at the last debate before the South Carolina presidential primary.

Newt Gingrich won the night on the first question, when he trained his fire on the media and debate moderator John King for focusing on claims by his ex-wife that Gingrich had requested an “open marriage.” He denied the allegations and received multiple standing ovations during the exchange. No other moment from the night was nearly as memorable. The rest of Gingrich’s night came in around par, but those first moments may be all he needed to capture the headlines and continue his recent momentum.

Rick Santorum also did well, landing a number of substantive punches on Mitt Romney for his Massachusetts health care program, as well as on Gingrich for his tenure as Speaker of the House. Santorum’s campaign has clearly done an effective job on their opposition research. He also gave some of the most detailed answers on policy questions and did his best to create some space between his positions and those of his opponents.

Romney once again had an average performance and stumbled when asked about releasing his federal income tax returns, which he finally committed to releasing in April. After two less-than-stellar debates in a row, it’s unclear whether he can hold on to his narrowing lead in South Carolina.

Ron Paul had great difficulty getting time in the debate and the other three candidates generally declined to engage him. At times his responses seemed to ramble.

Nate Silver doesn’t think Rick Perry’s endorsement of Newt Gingrich in
the Republican presidential primary will give Gingrich a direct boost,
but that’s not to say it doesn’t help advance the emerging “Newt-mentum”
narrative.

“Among these voters, second-place support was about
evenly divided among three candidates: Mr. Gingrich was listed by 22
percent of Mr. Perry’s supporters as their second choice, but Rick
Santorum and Mitt Romney were each listed as the second choice by 20
percent of Mr. Perry’s voters… And some of the ground that Mr.
Gingrich has gained there since Monday night’s debate has come at Mr.
Perry’s expense, so the voters who were most amenable to switching to
Mr. Gingrich may already have done so… Instead, the main way this may
aid Mr. Gingrich is by generating a strong headline for his campaign and
entrenching the sense among the news media that he has the momentum in
the race. That could be helpful to Mr. Gingrich given the complex story
lines of the past few days.”

Jonathan Chait: “Romney’s run of luck during the Republican nominating race is beginning to defy belief. Begin with the fact that Rick Santorum turns out to have won the Iowa caucuses. Finding this out now is approximately 0.001 percent as valuable as having it announced the night of the caucuses. There was an old Fed Ex commercial depicting an aging pool cleaner suddenly discovering a 20-year-old acceptance letter from Harvard he had never received, and imagining the life he could have had. That man is Santorum. He has to wonder if the Iowa vote counters were gay.”

A new Public Policy Polling survey in South Carolina — based on just one night of phone calls — shows Newt Gingrich leading Mitt Romney, 34% to 28%, followed by Ron Paul at 15%, Rick Santorum at 14%, Rick Perry at 5% and Buddy Roemer at 3%.

Key finding: “This is not a case of Romney imploding.  His support has been pretty
steady in the 28-30% range in our South Carolina polling so far. But
Gingrich has risen from 23% to 34% over the last two weeks, benefiting
from declining support for Santorum and also from undecided voters
moving into his camp.”

It’s the first of what will be three nights of tracking. PPP released the poll given Perry’s drop out from the race. It will be interesting to see how tonight’s debate and the interview with Gingrich’s ex-wife impact the results.

Mitt Romney’s campaign has attacked reports “on the candidate’s offshore investments, saying his holdings in the Cayman Islands and elsewhere have no effect on the amount he pays in U.S. taxes,” the Wall Street Journal reports.

“But the campaign’s assertions may be wrong or misleading. Tax experts said some of the offshore holdings are likely intended to help Mr. Romney avoid paying an obscure but hefty tax of as much as 35% on some of those investments, held in a tax-deferred retirement account.”

Marianne Gingrich told ABC News that when her husband Newt “admitted to a six-year affair with a congressional aide, he asked her if she would share him with the other woman, Callista.”

Said Marianne: “And I just stared at him and he said, ‘Callista doesn’t care what I do.’ He wanted an open marriage and I refused.”

The former Mrs. Gingrich says Newt began to plan a run for President at the time of the divorce and told her that Callista “was going to help him become President.”

Two new polls in South Carolina — both conducted after Monday’s presidential debate — show a very tight Republican primary race.

American Research Group: Newt Gingrich 33%, Mitt Romney 32%, Ron Paul 19%, Rick Santorum 9%, Rick Perry 4%.

InsiderAdvantage: Newt Gingrich 32%, Mitt Romney 29%, Ron Paul 15%, Rick Santorum 11%, Rick Perry 3%.

Caveat: Harry Enten makes a persuasive case that InsiderAdvantage has a pro-Gingrich bias to its results.

“Overall, I think it’s going to be pretty hard to argue that we have not executed a strategy over the last three years that has put America in a stronger position than it was than when I came into office.”

— President Obama, in an interview with Time magazine, on Mitt Romney’s criticism of his foreign policy.

Rick Perry will end his bid for the Republican presidential nomination today and endorse Newt Gingrich, the New York Times reports, “a decision that could influence the South Carolina primary on Saturday.”

“The announcement from Mr. Perry was expected to inject fresh momentum into Mr. Gingrich’s efforts to emerge as the leading alternative to Mitt Romney. It was unclear whether Mr. Perry would campaign with Mr. Gingrich in the final two days of the primary campaign here.”

David Brody: “There are a few lessons to be learned in the failed candidacy of Rick Perry. First of all, it doesn’t matter how many boxes you check (and Perry checked a lot of boxes) because if you can’t consistently articulate your message you’ve got no chance. You only get a certain amount of times you can make mistakes on the campaign trail before a narrative begins to form about you. Perry was way over the limit on mistakes.”