Sen. Harry Reid, D-NV, at a campaign rally in Las Vegas on Oct. 22. Hanging onto Reid's seat is a priority for labor unions. Ethan Miller/Getty hide caption

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Supporters listen as President Obama speaks during a rally for the Democratic National Committee at Ohio State University in Columbus on Sunday night. Saul Loeb/AFP/Getty Images hide caption

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President Obama shakes hands as he arrives at a rally Tuesday on the University of Wisconsin campus in Madison, Wis. Morry Gash/AP hide caption

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Ken Buck accepts the Republican nomination for Senate on Aug. 10 in Loveland, Colo. Buck, the Weld County district attorney, defeated former Colorado Lt. Gov. Jane Norton in the primary. Eric Bellamy/The Daily Tribune/AP hide caption

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