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As the Republican candidates play out their presidential nominating bids in three states on Tuesday, predictions are mounting that Rick Santorum will have a good night after pulling ahead in Midwestern polling.

But Mitt Romney still has the line on Colorado, which like Minnesota, is holding caucuses on Tuesday night that won't commit delegates but should provide some insight into the trajectory of the candidates. Missouri is holding a non-binding primary that sets up the standings for the delegate-awarding caucuses in a month from now.

According to Public Policy Polling, a Democratic firm, Santorum is leading in Minnesota, 33 percent to 24 percent for Romney. Newt Gingrich is at 22 percent and Ron Paul is at 20 percent.

In Missouri, Santorum leads the beauty contest 45-32 percent over Romney with 19 percent for Paul. Gingrich did not qualify to be on the ballot in Missouri.

The same polling firm shows Santorum with a possible second place finish in Colorado, behind Romney 37 percent to 27 percent with Gingrich at 21 percent and Paul at 13 percent.

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    Speaking to Fox News, Gingrich, who has been fighting hard against frontrunner Romney is back in polls, and conceded that he will finish somewhere in the middle of the pack.

    Gingrich plans to spend the day campaigning in Cincinnati, Dayton and Columbus, Ohio. He credited Santorum with skipping Nevada, which he says Romney had locked up long ago, and working on the states next in line. Gingrich said he's hoping to pick up a win in Texas, though he did not mention how the state's redistricting battle is setting back the timeframe for a vote. He added that he's prepared to take the race to California, which is scheduled for early June.

    But just because Gingrich is not on the battlefield doesn't mean Romney isn't trying to fire shots at the former House speaker. In an email sent Tuesday, Romney's camp said Gingrich "still has questions he needs to answer about his work" for mortgage guarantor Freddie Mac, particularly as Ohioans suffer during the housing crisis

    "Speaker Gingrich likes to compare himself to the Wright Brothers, but it's become increasingly clear that his vision for America isn’t taking flight with conservative primary voters," Romney spokesman Ryan Williams said.

    Romney's camp has also spared no quiver for Santorum, who was targeted Monday for his support for earmarks while a Pennsylvania senator. Romney has also tried to portray himself as the cultural conservative, which Santorum has used as a mantle of his campaign.

    In a radio interview, Romney said he supported the Susan G. Komen Foundation's decision to strip funding from Planned Parenthood. Komen later reversed that decision. In a rally near Denver, he said the Obama administration is forcing religious institutions to distribute "abortive pills."

    Santorum, who says he's not just about social issues, was holding a morning rally Tuesday in Colorado Springs, home to Focus on the Family. From there, he expects to campaign in Minnesota and then end his day in Missouri.

    But the Land of 10,000 Lakes could be where Santorum can really stake his claim since a first-place showing in Iowa, the first-in-the-nation caucuses.

    In the Public Policy Polling survey, Santorum's personal popularity is credited for his resurgence, with higher than 70 percent favorability in all three states. That's compared to Romney and Gingrich who fall in the 40s after a contentious fight in recents weeks.

    The poll also shows Santorum winning in all three of these states among Tea Partiers, evangelicals and those who describe themselves as "very conservative." That's a group Gingrich had been hoping to reach. Santorum said claims that the race is over are premature.

    "The idea that the challenger to Mitt Romney is Newt Gingrich, well that's reset," Santorum said, "or the idea that Mitt Romney is the 'hair apparent,'"

    But Paul, whose strategy is to win delegates that will influence the August convention, has been investing his time and money in Minnesota, moreso than any of his competitors. He was to hold a caucus-night party outside Minneapolis.

    In his Minnesota stops, Paul has hit on anti-war themes and cast himself as the candidate most committed to cutting government budgets. Four years ago, Paul won nearly 16 percent of the caucus vote to finish fourth in Minnesota, where Romney won.

    The Associated Press contributed to this report.