While Mitt Romney appears to be in solid shape in Colorado, Rick Santorum is gathering momentum in the latter two states and could deliver a surprisingly strong performance. Newt Gingrich, meanwhile, isn’t poised to have a good day: Recent polling has him running third in Colorado and Minnesota, and he’s not even on the ballot in Missouri.

As for Ron Paul, the Colorado and Minnesota caucuses offer an opportunity to rebound after under-performing in Nevada on Saturday.

Below are POLITICO’s five things to watch in Tuesday’s contests:

1) Santorum’s opening

If Santorum is ever going to offer a compelling case for staying in the race, the time to do it is Tuesday. He has a shot at winning two states, Minnesota and Missouri, which would provide a jolt of momentum at a time when Gingrich is flagging.

The deeply conservative Minnesota GOP — with its high percentage of evangelicals and social conservatives, it’s more like Iowa than Florida or New Hampshire — is built for a candidate like Santorum. While Romney won the caucuses easily in 2008, back then he was the more conservative alternative to McCain, whom he defeated by a nearly 2-to-1 margin. This time around, according to recent Public Policy Polling surveys, Santorum has the edge over Romney, with Gingrich and Ron Paul battling for third.

Just read between the lines of former Minnesota Gov. Tim Pawlenty’s Romney campaign press call Monday. Pawlenty declined to predict a winner, noted that Minnesota caucus-goers tend to “gravitate toward the perceived most conservative candidate,” and talked about the “different dynamics” of his home state. The fact that the Romney camp decided to hold a call pegged to Santorum was revealing in itself.

Missouri also figures to be favorable terrain, which is why Santorum will begin his Tuesday in Colorado but finish in Missouri, where he’ll hold his primary night party in St. Charles.

There’s no reason that Santorum can’t win there. Gingrich isn’t a factor and Romney and Paul haven’t paid the state much attention. And the former Pennsylvania senator’s message should have great appeal to Republicans in a state with a high percentage of evangelicals.

Missouri’s election is nothing more than a beauty contest, with no delegates up for grabs. But the stakes are still very high for Santorum. If he emerges as the victor in two races, on Wednesday he can point to three victories in the eight states that have voted so far — that’s two more wins than Gingrich.

If Santorum fails to win any state Tuesday, it’s a very different story, because if he can’t win in Missouri, where he has a clean shot at Romney and his rivals have mailed it in, where can he win?

2) Romney’s Colorado performance

Romney won big in Colorado in 2008, and it’s the state he’s best positioned to capture Tuesday. If he can’t win there, it could be a rough night for him.

The former Massachusetts governor has a solid organization in Colorado, deep and wide establishment support and a healthy lead in the polls. Romney losses in Minnesota and Missouri can be easily explained away. Not Colorado.

In a best-case scenario, Romney pulls off the trifecta Tuesday. Coming on the heels of big victories in Nevada and Florida, a Romney sweep would burnish his aura of inevitability. Winning Colorado, Minnesota and Missouri would give him, in the span of a week, a megastate win, and two victories in both the Mountain West and the Midwest. Most important, none of them were gimmes, like Nevada or New Hampshire.

3) Ron Paul and the caucuses

After Paul placed a disappointing third in Nevada, his showing in the Colorado and Minnesota caucuses will be closely scrutinized.

Paul has focused on caucus states that award delegates proportionally, a strategy that plays to his strengths and enables him to amass delegates during a long slog to the convention.

For that reason, he’s not even playing in Missouri’s primary beauty contest, which awards no delegates.

But his lackluster performance in Nevada, a caucus state where expectations were high for the Texas congressman, have raised questions about just how much he’s been able to expand his base. One way to put Nevada behind him would be to finish strong in Colorado and Minnesota, the two states that matter to Paul on Tuesday.

Of the pair, Minnesota appears more likely to deliver a favorable outcome. He won a respectable 16 percent there in 2008 — compared with 9 percent in Colorado — and he even managed to win a few counties.

4) Newt’s night

It’s going to be a bad night for Gingrich. The only question is how bad. At least he was smart enough to get out of Dodge — he’ll spend Tuesday campaigning in Ohio, rather than in any of the three states that are voting.

Gingrich isn’t on the ballot in Missouri, which gives Santorum a good shot at claiming at least one win. (It doesn’t matter that there are no delegates chosen there; this is still the momentum phase of the campaign).

Missouri might be easily dismissed, but Gingrich isn’t looking very steady in the caucus states either: There’s a chance he finishes fourth in Minnesota and a distant third in Colorado. None of it would be helpful on the heels of his Nevada performance and his much panned, post-results press conference there.

The road ahead doesn’t get any easier for him. It’s two long weeks until the next debate, when Gingrich can roll out the “new mechanisms” he promised to use against Romney. And after that, on Feb. 28, there are two primaries where Romney is presumed to have the edge — Arizona and Michigan.

5) Southwest Missouri

In 2008, the Missouri GOP primary was relatively close, with John McCain finishing on top, closely followed by Mike Huckabee and Romney.

In southwest Missouri, however, Huckabee cleaned up. In the part of the state sometimes referred to as “the buckle of the Bible Belt,” the former preacher and Arkansas governor won every county, including Springfield’s Greene County — home to the headquarters of the Assemblies of God, one of the largest Protestant denominations.

So if you want to measure the depth of the Romney resistance among evangelicals, this is the place to look.

In South Carolina, Santorum lost the Upstate battle for evangelical Christians to Gingrich. If the former Pennsylvania senator can’t run up the score in this part of Missouri with Gingrich absent from the ballot, it’s time to pack it in.