Republican presidential candidate Mitt Romney makes a pie shell with store owner Linda Hundt during a campaign stop Tuesday in DeWitt, Mich. Joe Raedle/Getty Images hide caption

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Iowans attend a marriage rally sponsored by The Family Leader on Tuesday at the Statehouse in Des Moines. The head of the organization says President Obama's endorsement of gay marriage could cost him the election. Charlie Neibergall/AP hide caption

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Vice President Biden defends the administration's foreign policy --€” and questions Mitt Romney's ideas — on Thursday at New York University. Lucas Jackson/Reuters/Landov hide caption

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Republican presidential candidate and former Massachusetts Gov. Mitt Romney speaks at a campaign rally in Tempe, Ariz., on Friday. Jae C. Hong/AP hide caption

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Courting Tea Party voters in Philadelphia on Monday night, Mitt Romney speaks next to a large statue of Benjamin Franklin at the Franklin Institute. Tim Shaffer/Reuters/Landov hide caption

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Rick Santorum won the Louisiana Republican presidential primary Saturday, beating front-runner Mitt Romney in the race to challenge President Obama. Jae C. Hong/AP hide caption

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A screen shot of President Obama from the trailer for his campaign's movie The Road We've Traveled. BarackObama.com/YouTube hide caption

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Peoria, Ill., as seen from across the Illinois River. Jeff Haynes/Reuters /Landov hide caption

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A supporter of Republican presidential candidate Mitt Romney holds a vintage campaign poster of Romney's father, George Romney, in Albion, Mich. Justin Sullivan/Getty Images hide caption

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Mitt Romney sings the national anthem before speaking at a Tea Party event at the Bakers of Milford Banquet Hall on Thursday in Milford, Mich. Scott Olson/Getty Images hide caption

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Mitt Romney shakes hands with supporters after a town hall meeting at Eagle Manufacturing in Shelby Township, Mich., on Tuesday. Andre J. Jackson/MCT/Landov hide caption

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Former Massachusetts Gov. and Republican presidential candidate Mitt Romney addresses supporters during a campaign rally at the Weber Paper Company Monday in Dubuque, Iowa. Chip Somodevilla/Getty Images hide caption

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