Republican presidential contender Mitt Romney campaigning in Ames, Iowa, on Thursday (Dec. 29, 2011). Chip Somodevilla/Getty Images hide caption

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A young Mitt Romney supporter holds yard signs Thursday at a campaign event at J's Homestyle Cooking in Cedar Falls, Iowa. Chip Somodevilla/Getty Images hide caption

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A volunteer arranges buttons before Mitt Romney speaks Wednesday in Clinton, Iowa. Chris Carlson/Associated Press hide caption

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A young supporter backs former Massachusetts Gov. Mitt Romney as he speaks on Wednesday at Homer's Deli and Bakery in Clinton, Iowa. Chris Carlson/Associated Press hide caption

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Former Speaker of the House Newt Gingrich complained about negative ads against him during a campaign stop at the National Toy Farm Museum on Dec. 27 in Dyersville, Iowa. Scott Olson/Getty Images hide caption

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Former Speaker of the House Newt Gingrich and former Massachusetts Gov. Mitt Romney chat after finishing a GOP debate in Sioux City, Iowa, earlier this month. Scott Olson/Getty Images hide caption

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In a last bout of campaigning before Christmas, Rep. Michele Bachmann of Minnesota signs autographs at the National Motorcycle Museum in Anamosa, Iowa, on Dec. 22. Charlie Riedel/AP hide caption

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