GOLDEN, Colo. (AP) -- Mitt Romney hopes his presidential campaign hasn't ignored Rick Santorum's aggressive attacks for too long, as caucuses in Colorado and Minnesota on Tuesday could reshuffle the race for the Republican presidential nomination.
Santorum largely bypassed Florida and Nevada to blanket the two caucus states with criticism of Romney and lay the groundwork among conservatives who have great sway in the process. Rival Newt Gingrich praised Santorum's strategy as shrewd even as he signaled he had no interest in exiting the four-way race, which also includes Ron Paul.
"I think that Santorum's going to have a pretty good day," Gingrich told reporters on the eve of the caucuses. "He targeted differently than I did. I stayed in Florida to fight it out. ... He took the same amount of time and energy and he came to Minnesota and Missouri and Colorado. For him, that was the right decision."
Missouri's GOP primary, also scheduled for Tuesday, promised Republicans a chance to show their allegiance to a candidate, but the effort is largely for show. No delegates will be awarded based on the outcome of the primary vote. Instead, Missouri will select delegates through a system of GOP caucuses and conventions that starts with local caucuses in mid-March. Moreover, Gingrich failed to get on the ballot in Missouri, which meant the vote there couldn't be read as a referendum on the former House speaker's viability.
Santorum, who for weeks has hammered Romney and Gingrich, seemed optimistic at his final campaign event before the contests got under way.
"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," Santorum said at a Denver rally.
Santorum seemed to spare Gingrich after the former House speaker suffered back-to-back losses to Romney in Florida and Nevada. With stepped-up intensity, Santorum castigated Romney as an unfit candidate and warned that Republicans were heading toward defeat if Romney were the nominee.
"A Romney nomination would not be in the best interest of us wining the general election and we need to have a conservative alternative. And my feeling is that Speaker Gingrich sort of had his chance in the arena and came up short in Florida and Nevada," Santorum told reporters in Golden on Monday. "And now it's our turn hopefully to get a one-on-one in Missouri."
Romney sensed a possible threat from Santorum on Monday and went after Santorum's time in the Senate as "not effective" because of his past support for spending on pork-barrel projects. Santorum flatly countered that Romney was "uniquely unqualified."
Clearly mindful of the late shift in the race, Santorum has been working aggressively in Minnesota and in conservative areas of Colorado in the past two weeks while Romney campaigned in Florida and Nevada. It was clear Monday that Santorum saw an opportunity to rise in the GOP race.
But he was also facing coordinated criticism from Romney's headquarters for the first time.
"Any time someone challenges Gov. Romney, Gov. Romney goes out and instead of talking about what he's for ... he just simply goes out and attacks and tries to destroy," Santorum said.