On Thursday night in Jacksonville, Fla., Mitt Romney (right) went after Newt Gingrich from the start on topics such as immigration and colonizing the moon. Matt Rourke/AP hide caption

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Iowa caucusgoers deposit their ballots on Jan. 3 at a school in Des Moines. On Thursday, the state GOP said it could not account for all votes from the caucuses. Jewel Samad /Getty Images hide caption

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Former Utah Gov. Jon Huntsman was surrounded by members of the media during a campaign stop earlier this month in Dover, N.H. Alex Wong/Getty Images hide caption

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Republican presidential candidate former U.S. Sen. Rick Santorum speaks to supporters after announcing that he was endorsed Saturday by the evangelical Christian leaders group. Mark Wilson/Getty Images hide caption

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The Republican presidential candidates duke it out at the NBC News-Facebook debate on Meet the Press on Sunday. Alex Wong/Getty Images hide caption

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Republican presidential candidates (from left) Ron Paul, Mitt Romney and Rick Santorum participate in the ABC News, Yahoo! News and WMUR Republican Presidential Debate at Saint Anselm College on Saturday in Manchester, N.H. Win McNamee/Getty Images hide caption

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Supercommittee member Sen. John Kerry, D-Mass., prepares Monday to speak with reporters in Washington as the deficit reduction panel's mandate ends in failure. J. Scott Applewhite/AP hide caption

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Obama is surrounded by former presidents in the Oval Office in 2009. Two of his predecessors — George W. Bush and Bill Clinton — won two terms, while two others — George H.W. Bush and Jimmy Carter — left office after just one.

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