As Romney breaks away from the pack, Rick Santorum hopes for an upset Rick Santorum autographs a supporter's sign after speaking at the Colorado School of Mines in Golden, Colorado on Tuesday. Photograph: Rick Wilking/Reuters Republican presidential candidate Rick Santorum is hoping to revive his campaign with a win in at least one of tonight's contests in Colorado, Minnesota and Missouri and upset front-runner Mitt Romney's steady progress towards the party nomination. Colorado and Minnesota hold their caucuses today while voters in Missouri hold a primary. Santorum, speaking at a rally in Denver on the eve of election day, said he had a shot of winning one of them. "This is a big day for us to see whether all the work that we put in in the past few weeks, when not so much attention was paid here as to Florida and Nevada, pays off," he said. Romney, in recognition of the possible threat posed by Santorum, switched from criticising Barack Obama to criticising Santorum on Monday. Campaigning in Colorado, he described him as a champion of pork-barrel spending, lobbying for federal funding for state projects, while he was a Pennsylvania senator. Former House Speaker Newt Gingrich opted against campaigning in any of the three states holding contests today, possibly in recognition that they are a lost cause for him. Before leaving Colorado Monday, he predicted: "I think that Santorum's going to have a pretty good day tomorrow, and he will have earned it." Gingrich has shifted his attention to the Super Tuesday states, in particular Ohio, where he was scheduled to campaign today. Ten states will be in play on Super Tuesday on March 6. Unlike the January contests, there have been relatively few polls in Colorado, Minnesota and Missouri. Of those that have carried out surveys, PPP, based on polling conducted Sunday and Monday, found Santorum with a 9% lead over Romney in Minnesota, 33% to 24%. In Colorado, PPP found Romney had a 10% lead over Santorum, 37% to 27%. PPP, in a survey conducted Monday, found Santorum with a 13% lead over Romney in Missouri, 45% to 32%. Santorum won the first of the contests in Iowa on January 3, fighting on a deeply social conservative platform that appealed to Christian evangelicals, but failed to make any impression in the following four contests. His social conservative views could be more attractive to voters in Minnesota and Missouri, and in parts of Colorado, such as the stronghold of Christian evangelicals in and around Colorado Springs. Santorum was in danger of being squeezed out of the presidential debates by Romney and Gingrich but made a series of forceful interventions, aimed mainly at Romney's health care reforms while governor of Massachusetts, regarded by many conservatives as similar to Barack Obama's healthcare reform. The winner of the Republican nomination needs 1,144 delegates to the party convention in Tampa in August. The Associated Press, which keeps a running tally of delegates awarded so far, has Romney on 101, Gingrich 32, Santorum 17 and Paul 9. Colorado has 36 delegates at stake and Minnesota 40. Missouri has no delegates up for grabs tonight. Its convention to choose delegates is not until March 17 and it only decided to hold its primary to try to seize a share of media attention. The fourth candidate in the race, Ron Paul, opted against devoting resources to the Florida primary on January 31 to focus on the caucus states such as Nevada, Minnesota, Colorado and Maine, which completes its caucuses on Saturday. But so far the strategy has failed to pay off, with Paul coming third in Nevada.