Polls show a Newt Gingrich comeback? Not so fast.

Newt-mentum, catch it! Are polls showing that due to his fiery performance in Monday’s GOP debate Newt Gingrich is closing the gap on front-runner Mitt Romney?

Well, there is some evidence that may be the case. But it is preliminary, and may actually reflect a tightening of the race that has been underway for some time.

First up is a new CNN/Time poll, which finds that, in South Carolina, Mr. Romney is now the choice of 33 percent of likely Republican voters, down from 37 percent in early January. Ex-Speaker Gingrich, by contrast, is now the choice of 23 percent of GOP South Carolinians, up from 18 percent in the previous survey.

Yes, this poll shows that something may be going on. But as polling expert Nate Silver of The New York Times notes on his Twitter feed, pollsters started work on this survey on Jan. 13, so it’s impossible to tell whether there’s been a sharp rise in support for Gingrich since the debate.

It’s possible that the gap is even closer than the CNN results show. If it isn’t, Gingrich still looks likely to finish in second place: a 10-point gap is fairly large with only days to go before the vote.

Mr. Silver tweets that Insight LLC has showed him a poll that shows big movement toward Gingrich, but has small sample size. Again, that would be a hint of something, but not a definitive proof.

Bottom line: Silver has adjusted his rolling prediction of South Carolina’s results. He now says Gingrich has an 11 percent chance of winning, up from 8 percent. Romney’s chance of victory is 87 percent, according to Silver.

Which, we will point out, is pretty high. But not 100 percent, by any means.

Meanwhile, national polls are showing mixed signals about Newt-mentum at the moment.

Gallup’s five-day rolling average still has Romney with a comfortable lead over Gingrich, 33 percent of voters to 16 percent. That’s down a few points over the last three days.

Rassmussen Reports has a snap poll out Wednesday that shows much bigger movement, however. It puts Romney only three points ahead of Gingrich, 30 to 27.

The bottom line? There’s somethin’ happenin’ here. What it is, ain’t exactly clear.