U.S. Senate candidate Elizabeth Warren, a Democrat, greets people at Dinky's Blue Belle Diner in Shrewsbury, Mass., on Sunday. Steven Senne/AP hide caption

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Republican presidential hopeful Ronald Reagan, right, listens to the Rev. Jerry Falwell during a campaign stop in Lynchburg, Va., in October 198 Charles Harrity/AP hide caption

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Republican presidential candidate Mitt Romney campaigns with Sen. Kelly Ayotte on Monday in Portsmouth, N.H. A 43-year-old freshman senator, Ayotte is among those under consideration as a vice presidential running mate, according to a Romney adviser. Jim Cole/AP hide caption

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President Obama and former President Bill Clinton golf together in September 2011. The former president is campaigning for Obama, four years after the two men exchanged harsh words during the Democratic primary battle between Obama and then-Sen. Hillary Clinton. Chris Kleponis-Pool/Getty Images hide caption

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