Colorado, Minnesota and Missouri all hold contests Tuesday, making it the first day of the 2012 campaign that multiple states deliver a verdict. 
 
 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. 
 
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 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. 

 Mitt Romney returned to the campaign trail here Monday and trained his focus on President Obama, but his top aides and key surrogates fought to beat back a possible surge by Rick Santorum on the eve of Republican presidential contests in a trio of states. 
 
 Romney’s aides and a top surrogate, former Minnesota governor Tim Pawlenty, unloaded on Santorum over his support of taxpayer-funded earmarks during his years in Washington, calling him a “champion of earmarks.” The Romney team lobbed similar broadsides against Newt Gingrich ahead of last month’s Florida primary, but have let up somewhat as the former House speaker’s campaign has struggled. 
 
 Santorum threw some salvos of his own, assailing Romney’s health-care record as Massachusetts governor and saying he is “simply dead wrong on the most important issue of the day and should not be the nominee of our party.” 
 
 In a speech he delivered across the street from the Mayo Clinic in Rochester, Minn., Santorum added that a Romney nomination would be a “devastating thing” for Republicans, according to the Associated Press. 
 
 A couple of hours later, Romney campaign aides shared with reporters comments Santorum made in 2008 when he was backing Romney in that presidential race. “If you’re a conservative, there really is only one place to go right now . . . and that’s Mitt Romney,” said Santorum, a former senator from Pennsylvania. 
 
 The Romney team has not unleashed such attacks on Santorum since his narrow win in the Iowa caucuses last month. As of Monday, the campaign was not airing any paid negative advertisements about Santorum. 
 
 Romney did not mention Santorum or any other Republican rival in his Monday afternoon rally in Grand Junction. He preserved his rhetorical fire for Obama, telling a crowd of a few hundred here: “Based upon the president’s own standard, he has failed. He does not deserve a second term.” 
 
 But in an interview with WCCO Radio in Minneapolis, he said, according to the AP, that Santorum’s “policies are, in my view, those of many Republicans in Congress who went along with Democrats to raise the debt ceiling, to allowing earmarks and to growing the size of federal government to a level that is frankly choking off the capacity of our economy to grow at the rate it should.” 
 
 Santorum accused Romney of throwing “the kitchen sink” at him. “He simply goes out and tries to destroy,” Santorum told reporters in Minnesota. “I don’t think it’s going to work this time.” 
 
 Santorum finished last among the four major candidates in Nevada’s GOP caucuses on Saturday, but he has devoted considerable time to the three states that will vote Tuesday. He said Sunday that he thinks he can do “exceptionally well” in Missouri’s nonbinding primary and “very well” in caucuses in Colorado and Minnesota. 
 
 He hopes a strong finish can provide a fresh jolt to his candidacy, which has struggled to raise money and build a national organization that can compete with Romney’s more formidable operation. 
 
 As the campaign moved onto multiple fronts this week, the candidates were forced to choose where to focus their time and money. Gingrich spent Monday campaigning in Colorado and Minnesota, while Rep. Ron Paul (Tex.) held rallies in Minnesota. 
 
 Romney was scheduled to stump in Minnesota, but abruptly canceled those plans so he could spend time in Colorado, where he has a robust organization and is considered the favorite. 
 
 Although the three contests could give winners momentum, they are nonbinding and will not award delegates, according to the Republican National Committee. Colorado’s 36 delegates will be chosen at district conventions in the spring. Minnesota will award 40 delegates at district conventions in April. And Missouri’s primary is merely a “beauty contest” — the state’s 52 delegates will be chosen beginning with precinct caucuses on March 17. 
 
 Romney’s prospects for a clean sweep of the three states were unclear Monday. Gingrich did not make it on the ballot in Missouri, which could help Santorum consolidate conservatives. And in Minnesota, whose caucuses Romney won in 2008, public polling showed Santorum running strong, but polls have been inconsistent and are considered unreliable. 
 
 Both states will be important barometers for Romney’s support in Midwestern swing states, but the candidate’s advisers tried to play down his chances. 
 
 “It’s a relatively small turnout, and the caucus attendees here tend to gravitate to the most conservative candidate,” Pawlenty said in a conference call with reporters. He quickly corrected himself to say “the most perceived conservative candidate.” 
 
 Pawlenty noted that in 2008, about 60,000 voters turned out for Minnesota’s GOP caucuses. If a similar share participates this time, it would represent about 2 percent of the state’s 3 million registered voters. He said all four candidates could be “bunched together toward the top of the pack.” 
 
 Staff writer Felicia Sonmez in Washington contributed to this report.
– Colorado, Minnesota, and Missouri will all get a chance to weigh in on the Republican presidential nomination today, in a day that might just change the momentum for Rick Santorum's campaign. Here's what to watch for: Santorum's surge: If Santorum is going to make a move, now's the time. According to the latest Public Policy Polling numbers, he's in first, ahead of Mitt Romney, in both Missouri (45% to 32%) and Minnesota (33% to 24%). He's even second in Colorado. 'Champion of earmarks': Team Romney is at least a little worried, because surrogates bashed Santorum yesterday as a "champion of earmarks," the Washington Post reports. Then again, they haven't resorted to negative ads… Beauty pageants: …Possibly because only momentum is at stake here. All three contests are non-binding, and Missouri's is a pure "beauty pageant," with all the actual delegates being awarded in precinct caucuses in March. Newt Gingrich's plunge: But momentum still matters, and Gingrich is about to lose a lot of it. He's not even on the ballot in Missouri and isn't polling well in the other two states, with fourth-place finishes distinctly possible. Ron Paul's caucus gambit: The libertarian gadfly's strategy revolves around caucus states, so after a lackluster showing in Nevada, he needs to do well in today's caucuses in Minnesota. 'Buckle of the Bible Belt': That's a nickname for Southwest Missouri, and with good reason. If you want to know if Romney has a problem with evangelicals, Politico advises watching the results here.