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Photo by: Steven Senne

** FILE ** Republican presidential candidate, former Massachusetts Gov. Mitt Romney, left, shakes hands with U.S. Rep. Paul Ryan, R-Wis., chairman of the House Budget Committee, right, before speaking with supporters of Wisconsin Republican Gov. Scott Walker at a phone bank during a campaign stop in Fitchburg, Wis., in this March 31, 2012, file photo. (AP Photo/Steven Senne, File)

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