Rick Santorum's unlikely sweep of three Republican contests on Tuesday punctured the aura of inevitability surrounding Mitt Romney's claim to the nomination and nursed the niggling perception that the front-runner can't close the deal with conservatives.

Romney won Minnesota and Colorado in his 2008 presidential bid. On Tuesday, he came in third and second place, respectively. He also lost to Santorum in Missouri.

For Santorum, the trifecta reaped bragging rights but no convention delegates, and it may provide only a fleeting burst of money and momentum for his shoestring campaign. For Romney, who ignored Missouri and downplayed Minnesota, the losses are probably little more than speed bumps on his road to the nomination. He is the only GOP contender with the money and organization demanded of a national campaign that could drag on for months.

But the results on Tuesday give his rivals an opening to keep contesting the nomination and fodder to President Obama's reelection campaign as it seeks to dampen enthusiasm for its likely opponent. The results also showed that the conservative grassroots are pulling the strings in this race, despite efforts by the Republican establishment to annoint Romney.

There are still a few twists and turns left in this primary.

"Tonight's victory should put to bed the idea that the Republican nomination for Mitt Romney is inevitable," said Stuart Roy, an advisor to a super-PAC backing Santorum, after the former Pennsylvania senator was declared the winner in Missouri.

The chairwoman of the Democratic National Committee, Rep. Debbie Wasserman Schultz of Florida, also gloated. "Tonight was a bad night for Mitt Romney, plain and simple,'' she said in a statement after Minnesota also put Santorum on top. "What should have been a night where he began to consolidate Republican support instead has shown that Republicans are reluctant to get behind him.''

And that was before the news broke that Romney also lost Colorado, a state he seized with 60 percent of the vote in 2008 and expected to win again, as evidence by his decision to spend Tuesday night in Denver. Santorum and Romney took turns leading as the results trickled in after midnight, the agonizing wait reminiscent of their neck-and-neck contest in Iowa. Romney was initially named the winner in Iowa by 8 votes. Seventeen days later, the state party said Santorum had surpassed him by 34 votes.

And like in Iowa, Santorum's success on Tuesday suggested that it pays to show up. He spent the most time of all of the candidates in the three states and virtually had Missouri to himself. Newt Gingrich, long viewed as the bigger threat to Romney, did not even qualify for the ballot in that state. His absence there and thin appeal in Minnesota and Colorado will seriously erode his claim that the race is a two-man contest between him and Romney. Giving away his lack of confidence, he spent Tuesday campaigning in Ohio on the first day of early voting.

"The results tonight are bad news for Newt, but not fundamental game changers,'' said Republican strategist Phil Musser, who is supporting Romney. "It's now clear the race will progress well into the spring, and Romney continues to have a laser-like focus on winning where it matters, as opposed to winning where it is nice.''

Tuesday also dealt setbacks to Ron Paul, the libertarian congressman from Texas who has focused on mobilizing supporters in caucus states. He came in second place in Minnesota and fourth place in Colorado.

The one-two-three punch by Santorum felt particularly jarring since he hasn't won a contest since his come-from-behind finish in the Iowa caucus on Jan. 3. Santorum derived little momentum from the caucus, partly because the state party initially declared him a runner-up and partly because he was ill-prepared for the next contests in New Hampshire, South Carolina, Florida and Nevada. On Tuesday, he finally got to deliver the victory speech he was robbed of in Iowa.

"Wow!'' Santorum told a cheering crowd in St. Charles, Missouri, before the Colorado votes were tallied. "Conservatism is alive and well in Missouri and Minnesota.''

Republicans in these states are known for their socially conservative views, and Santorum has stressed his opposition to abortion and the importance of traditional marriage more than any other candidate. In contrast, Romney, a Mormon who once took moderate positions on abortion and gay rights, has struggled to win over the Christian conservatives who dominate many GOP contests.Those voters presumably boosted Santorum to victory, as they did for Gingrich in South Carolina. Even in Florida, where Romney won handily, Gingrich beat him among the most conservative voters and the strongest supporters of the tea party.
 
Romney had sought to tamp down expectations for Tuesday's contests. His campaign stressed that no delegates would be awarded in any of the three contests and called Missouri "strictly a beauty contest.'' The caucuses in Colorado and Minnesota were only a first step toward naming delegates to the party's national convention, while Missouri's primary was only for show; the state will hold caucuses next month.

In a sign that the Romney campaign saw a Santorum surge looming, it dispatched a top surrogate, former Minnesota Gov. Tim Pawlenty, to attack the former Pennsylvania senator on Monday, after weeks of aggressively targeting Gingrich.

"This was a good night for Rick Santorum,'' Romney said in Denver before the results were tallied in that state, "but I expect to become our nominee with your help.''  He added at the end of his speech, "We've got a long way to go.''