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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Mitt Romney greets patrons at a restaurant called The Mitt in Mount Clemens, Mich., on Friday. The candidate hasn't done as much handshaking lately, given the size of the recent primary states. Gerald Herbert/AP hide caption

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Republican presidential candidate Mitt Romney addresses the Conservative Political Action Conference (CPAC) in Washington, Friday. Evan Vucci/AP hide caption

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Republican presidential hopeful Mitt Romney won the Nevada caucus Saturday, maintaining strong front-runner status in the race to the nomination. Emmanuel Dunand/AFP/Getty Images hide caption

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Romney supporters gather for a rally at the Elko Regional Airport in Nevada on Friday. The state holds its caucus Saturday. Justin Sullivan/Getty Images hide caption

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Former Massachusetts Gov. Mitt Romney campaigns at Ring Power Lift Trucks in Jacksonville, Fla., on Monday. Polls show him widening his lead in Florida after adopting a more aggressive campaign style. Charles Dharapak/AP hide caption

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President Obama waves after speaking at a UPS facility in Las Vegas on Thursday. Nevada is one stop on the president's latest road trip focusing on the economy. Julie Jacobson/AP hide caption

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Newt Gingrich arrives for a GOP presidential candidate forum Saturday in South Carolina. Gingrich had to be reminded of the rules not to mention rivals by name, but was still able to continue criticism of Mitt Romney. Joe Raedle/Getty Images hide caption

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Mitt Romney speaks during a Chamber of Commerce breakfast Monday in Nashua, N.H. Justin Sullivan/Getty Images hide caption

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Former Massachusetts Gov. Mitt Romney pleaded with his supporters at a rally Monday in Dubuque, Iowa, saying, "I need every vote." He did — winning the Iowa caucuses the next day by just eight votes. Chip Somodevilla/Getty Images hide caption

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Former Massachusetts Gov. Mitt Romney greets voters after speaking at the Mississippi Valley Fairgrounds on Wednesday in Davenport, Iowa. Win McNamee/Getty Images hide caption

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President Obama, Vice President Joe Biden and members of his National Security team receive an update on the mission against Osama bin Laden in the Situation Room of the White House. A classified document seen in this photograph has been obscured. Pete Souza/White House hide caption

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