President Obama greets patrons at Ross' Restaurant in Bettendorf, Iowa, on Tuesday. In 2008, the president's unexpected victory in the state helped propel his campaign. Saul Loeb/AFP/Getty Images hide caption

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U.S. Rep. Michele Bachmann greets Irene Blom before speaking at a Presidential Lecture Series sponsored by The Family Leader, April 11, 2011 in Pella, Iowa. Bachmann, along with Herman Cain, Newt Gingrich, Gary Johnson and Rick Santorum, are expected to drop in on a Tea Party Bus Tour making its way through Iowa. Charlie Neibergall/AP hide caption

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Then-Democratic presidential hopeful Barack Obama waves during a May 24, 2008, campaign stop in San Juan, Puerto Rico. Keeping a campaign promise, Obama returns Tuesday. Brennan Linsley/AP hide caption

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Republican presidential hopeful, former Mass. Gov. Mitt Romney meets with entrepreneurs at Bizdom U in Detroit on Thursday. Bizdom U is a business development center to help entrepreneurs start up businesses in the state. Carlos Osorio /AP hide caption

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Corn is big business in Iowa, which has usually made anything but support for ethanol subsidies off-limits for presidential hopefuls. Steve Pope/AP hide caption

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Former Massachusetts Gov. Mitt Romney focuses on a key issue — corn — in Ankeny, Iowa, on Friday, as he prepares to launch his 2012 presidential bid. Charlie Neibergall/AP hide caption

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