Could Rick Santorum put Newt Gingrich in the rearview mirror Tuesday?

Tuesday night is shaping up to be a good night for Rick Santorum.

While polling has been limited in the three states holding contests Tuesday (Colorado, Minnesota, and Missouri), and an unusually high number of voters are uncommitted, pollsters are predicting that Mr. Santorum will win two out of the three and should place a close second to Mitt Romney in Colorado.

The question is: Will that be enough to revive Santorum's candidacy or even put him on a path to nomination?

Despite winning (barely) Iowa's caucuses a month ago, Santorum has been largely an also-ran in the early contests, barely getting mentioned by headlines more interested in Romney, Newt Gingrich, and Ron Paul.

So why is the former Pennsylvania senator surging now?

Likeability might be one factor. According to a recent Public Policy Polling report, responsible for the most up-to-date polls in the three states voting today, Santorum has a favorability rating over 70 percent in all three states. That's in marked contrast to Romney (with favorability ranging from 47 to 60 percent) and Mr. Gingrich (47 to 48 percent).

Santorum's biggest appeal, according to PPP, is with tea partyers, Evangelicals, and voters who describe themselves as "very conservative" – all groups who had been leaning toward Gingrich, but now seem to be abandoning him for Santorum.

There are positive signs in other polls as well. While Santorum still trails both Romney and Gingrich in national polls, Gallup's daily tracking poll now has him only six points behind Gingrich, who is falling. And a new Rasmussen poll that tracks how all four candidates do in potential matchups against President Obama has Santorum as the only candidate who comes out ahead, 45 percent to 44 percent (a finding Santorum's campaign has highlighted as much as they can).

Another reason for Santorum's resurgence may be Gingrich's descent. More conservative voters seem to be getting over their Gingrich crush and, still unhappy with Romney as a nominee, are moving to Santorum. Gingrich's decision not to make any campaign appearances in Minnesota this past week – one of the few states where he might have had a chance – only helps Santorum.

(In Missouri, whose nonbinding primary Tuesday has been likened to a "beauty contest" before the actual delegate-choosing caucuses in a month, Gingrich isn't even on the ballot – another point in Santorum's favor.)

But before anyone starts speculating about the possibility of a real battle between Santorum and Romney, there are some big caveats.

For one thing, the contests Tuesday are relatively small ones – only getting attention in the February desert of the GOP primary season – and don't even mean much for delegate counts. Colorado and Minnesota's caucuses are nonbinding, with delegates actually selected when the state party holds conventions later in March or April.

Santorum faces massive hurdles ahead when it comes to fundraising and organization against the better prepared Romney team. He also needs to convince voters that he can talk about the economy as well as he can talk about conservative social issues, and that he actually has a possibility of becoming the nominee. And he has to hit hard against Romney's weaknesses without going so negative that he loses that likeability edge – a tall order.

Santorum has already stepped up those attacks, hammering away at Romney for his Massachusetts healthcare program, in particular. In Minnesota this week he argued that "RomneyCare" makes Romney "uniquely unqualified" from being the nominee.

But Romney is stepping up his attacks too, and now has Santorum in his sights, largely ignoring Gingrich and Paul. He even had Minnesota Gov. Tim Pawlenty hold a conference call with reporters Monday just to bash Santorum, calling him a "champion of earmarks."

It's becoming harder and harder to envision a GOP nominee other than Romney – even if Santorum slows his momentum Tuesday night and keeps the uncertainty going. But Santorum does have a few influential conservatives pulling for him.

A strong showing by Santorum Tuesday, argues William Kristol in the Weekly Standard, would do the most to slow the "Romney juggernaut." "It would also of course help Santorum's chances to replace Gingrich down the road as the alternative to Romney – an outcome that, I suspect, might well result in a better race for the nomination and a healthier situation for the ultimate Republican nominee," he writes.

The Washington Post's Jennifer Rubin, meanwhile, outlines in her Right Turn blog all the hurdles Santorum would have to clear to get the nomination – which she agrees are a lot. But she concludes:

"The right made a critical error in not recognizing Santorum’s strengths earlier in the race. But time is not his greatest enemy, and it’s not useful for him to dwell on why conservative pundits went chasing after defective contenders. What he now has to do is grow in stature, project himself as Romney’s equal and convince conservatives that they can not only improve their chances of winning back the White House but also get a more consistent conservative if they jump from the Romney ship... But if anyone in the GOP field (past or present) can do it, Santorum’s the guy."