U.S. Republican presidential hopeful Rick Santorum has shaken up what was largely thought to be a settled race by scoring three wins over Mitt Romney, but might find it hard to compete with the well-funded front-runner in coming primaries.

Santorum, a staunch social conservative and former Pennsylvania senator, stunned observers and the Republican establishment by adding Colorado to his win column on Tuesday night, hours after solidly winning the Minnesota caucuses and the Missouri primary.

What's next in the Republican nomination race:

Feb. 11: Maine (caucus).

Feb. 28: Arizona (primary); Michigan (primary).

Tuesday night's state contests are largely meaningless because they awarded no delegates to Santorum for him to take to the Republican national convention in Tampa, Fla., in August. Missouri will award its delegates after it holds separate caucuses in March.

Santorum, whose shoestring campaign has not won a state since the Iowa caucuses in December, can now claim some momentum going into the next contest and try to convert it into campaign contributions. 

In another sign he was looking beyond the primaries, Santorum told supporters in Missouri on Tuesday night he didn't "stand here to be the conservative alternative to Mitt Romney."

"I stand here to be the conservative alternative to Barack Obama," he said to cheers.

Romney, who entered Tuesday's contests fresh from a win in the Nevada caucuses and a trouncing of widely viewed main rival Newt Gingrich in Florida, now finds himself facing renewed questions over his ability to win over conservative voters in the wake of the three defeats.

In an additional blow, Romney came in third in Minnesota behind solid second-place finisher Ron Paul, the libertarian Texas congressman with an avid grassroots following of volunteers.

Long race could help or hurt Romney

Romney still leads all candidates in the delegate count, but Santorum has now won more states and achieved it with a fraction of the millions the Romney campaign has spent on advertising — both positive and negative.

While Romney's wins have come in bigger states with more media markets, Santorum has found success in states like Minnesota, where a personal appearance generates "earned media" — or news coverage of a candidate's event that spreads throughout a market.

"It's an indication of what personal appearance time can do for you," Michael Traugott, a political science professor at the University of Michigan, told CBC News on Wednesday.

"Santorum didn't have much money, but he made up for it by spending time in these states."

Aside from next week's Maine caucuses, and Michigan and Arizona holding their primaries on Feb. 28, the primary calendar now faces a significant gap of major events up until March 6, also known as Super Tuesday. That's when 10 states, including potential swing states Ohio and Virginia, hold votes.

This gap could prove useful to Santorum, and even Gingrich, who can devote more time to the Michigan and Arizona races and build name recognition and spark turnout, instead of being forced to contend with multiple races in rapid succession, which would favour a front-runner with more money, like Romney.  

"Santorum woke up this morning and said, 'Now I want to spend some time in Michigan,'" Traugott said.

Romney's campaign budget still dwarves his rivals' and has the advantage of on-the-ground operations in every primary and caucus state coming up. But a long race could prove to be a double-edged sword for the front-runner.

As long as two social conservatives are in the race, Romney can expect to split the vote, and in turn, use the race to groom his campaigning skills, similar to what observers believe Barack Obama did in the 2008 Democratic nomination race against Hillary Clinton.

The contest between Santorum and Gingrich for more conservative voters helps Romney split the vote, but also subjects him to the most enduring and withering attacks.

"I think it's pretty clear in the last couple of weeks that Romney has become a better candidate because of the challenges he faces," Traugott said. "On the other hand, the longer the race goes on, the more nuggets are being provided for Democratic advertising in the fall."

The Romney camp is expected to step up its criticism of Santorum as a Washington insider with a dubious record of earmarking federal money for his home state. Santorum has been the most effective of Romney's rivals in his questioning of Romney's state health-care plan, which the Democrats have cited as inspiration for Obama's national plan.

Speaking Wednesday in Atlanta, Romney said the Tea Party movement was created to fight Washington insiders who spend too much and that Santorum and Gingrich "are the very Republicans who acted like Democrats."

Santorum, who has defended Romney in the face of Gingrich's criticisms over his record as a successful investment banker, urged Republicans not to cede the so-called ObamaCare issue to the Democrats in the November general election by selecting Romney as their nominee.  

The Democrats, in a sign they still believe Romney will be Obama's eventual opponent, immediately used Santorum's wins to hit out at the former Massachusetts governor, saying Tuesday night's "embarrassment" shows Romney was rejected by a large portion of the Republican electorate.

Meanwhile, Gingrich, a former Georgia congressman and Republican House Speaker in the 1990s, finds himself again barraged with questions over what chances he has of winning the nomination.

Gingrich, who previously suggested Santorum withdraw from the race to allow conservatives to rally behind him and defeat Romney, has vowed to stay in the race until the August convention.

"Gingrich, I think, can only do damage to others at this point," Traugott said.  

The candidate made no mention Wednesday of his poor showings, telling workers at a metal manufacturing plant in Ohio that he can lead the nation to an era of prosperity and security.

With files from The Associated Press