Republican presidential candidate Mitt Romney pauses during a visit to St. Paul's Lutheran Church while campaigning in Berlin, N.H., on Dec. 22. Charles Krupa/AP hide caption

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Mitt Romney narrowly won in Michigan Tuesday night. For Super Tuesday, he'll set his sights on Ohio, Massachusetts, Vermont and Virginia. Bill Pugliano/Getty Images hide caption

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Mitt Romney, back in his Bain Capital days. David L. Ryan/Boston Globe via Getty Images hide caption

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Following a visit to his Michigan campaign headquarters on Feb. 28, Mitt Romney told reporters that Republican voters should choose the party's nominee. Justin Sullivan/Getty Images hide caption

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In a final bit of campaigning before Tuesday's vote, Mitt Romney and his wife, Ann, wave to his supporters during a campaign stop in Royal Oak, Mich., on Monday night. Rebecca Cook /Reuters /Landov hide caption

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Polls show Rick Santorum and Mitt Romney in a tight race heading into Tuesday's Michigan primary. Santorum's campaign signs are stuck in the snow before his campaign stop at the The Colonial Valley Suites on Feb. 26 in Davison, Mich. Joe Raedle/Getty Images hide caption

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