GOP candidates Rick Santorum and Mitt Romney

GOP candidates Rick Santorum and Mitt Romney (CNN)

(CNN) -- Rick Santorum awoke to a new reality Wednesday after sweeping all three Republican presidential contests a day earlier, reshaping the contest that will decide who runs against President Barack Obama in November.

Santorum won caucuses in Minnesota and Colorado, as well as a nonbinding primary in Missouri to energize his campaign and raise questions about front-runner Mitt Romney's ability to attract broad conservative support.

The victories by Santorum bolstered his contention that he is the strongest conservative challenger to the more moderate Romney for the GOP nomination, and the most formidable conservative candidate to take on Obama.

"I don't stand here and claim to be the conservative alternative to Mitt Romney," Santorum declared to cheering supporters outside St. Louis. "I stand here to be the conservative alternative to Barack Obama."

Colorado was the most competitive state of the day, with Santorum winning 40% of the vote to 35% for Romney, 13% for former House Speaker Newt Gingrich and 12% for Texas Rep. Ron Paul.

After a night of returns trickling in and the lead shifting between Santorum and Romney, Colorado Republican Party chairman Ryan Call announced live on CNN that Santorum was the winner.

In Minnesota, Santorum got 45% of the vote to 27% for Paul, 17% for Romney and 11% for Gingrich, with 88% of the total counted, according to the secretary of state.

The victory in a state Romney won in his unsuccessful 2008 presidential bid was a strong statement by Santorum that he represents a major conservative challenge to both Romney and Gingrich.

However, a low turnout in all three races signaled possible dissatisfaction among Republican voters with the candidates.

All the 70 delegates available Tuesday came from the Minnesota and Colorado caucuses, while the Missouri primary was nonbinding with no delegates at stake.

The two caucus states didn't officially award delegates Tuesday night -- that will happen down the road at district and state conventions -- but the news media, including CNN, will use them to make unofficial delegate count estimates.

With 100% of the Missouri vote counted, Santorum had 55% to 25% for Romney and 12% for Paul, according to unofficial results. Gingrich didn't make the ballot in Missouri.

Such a dominating victory by the conservative Santorum showed his appeal to Missouri's large blocs of evangelical and tea party supporters.

"Conservatism is alive and well in Missouri and Minnesota," Santorum declared before the Colorado count had been completed.

While Tuesday was a stunningly successful night for Santorum, it was a terrible night for Romney and Gingrich, who has been competing with Santorum for the support of conservatives against the more moderate Romney.

Gingrich spent little time or money in the three states, instead focusing his now limping campaign on the Super Tuesday contests of March 6 that will be worth more than 400 delegates from 10 states.

Romney, however, campaigned hard in Colorado and to a lesser degree Minnesota, and the stinging losses cost him any momentum from his two straight victories in Florida and Nevada prior to Tuesday.

A senior adviser to Romney signaled the campaign would take a tougher approach toward his resurgent rival and portray him as a Washington insider.

"Look, I just don't think it's a time when people are looking to Washington to solve problems with Washington," senior Romney adviser Stuart Stevens said of Santorum, a former U.S. senator.