Colorado Republican Rep. Cory Gardner officially announces his candidacy for the U.S. Senate at Denver Lumber Co. on March 1. Gardner will run against Democratic incumbent Mark Udall. Chris Schneider/AP hide caption

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Sen. Lindsey Graham of South Carolina voices his opposition to President Obama's choice of former Sen. Chuck Hagel of Nebraska as secretary of defense, on Capitol Hill last week. J. Scott Applewhite/AP hide caption

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President Obama nominates former Sen. Chuck Hagel, R-Neb., to be defense secretary Monday at the White House. Mark Wilson/Getty Images hide caption

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House Speaker John Boehner arrives at the White House on Friday for talks with President Obama and congressional leaders aimed at avoiding the "fiscal cliff." Mandel Ngan/AFP/Getty Images hide caption

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Sen. Jon Tester, D-Mont., receives a kiss from his grandson Wednesday in Great Falls, Mont. Tester won re-election in a tight contest with Republican Rep. Denny Rehberg. Michael Albans/AP hide caption

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Sen. Marco Rubio, R-Fla., delivers a speech during the annual Conservative Political Action Conference in February in Washington. Win McNamee/Getty Images hide caption

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