Marine Corps Commandant Gen. Joseph Dunford Jr. testifies Thursday during his Senate Armed Services Committee confirmation hearing to become the chairman of the Joint Chiefs of Staff. Cliff Owen/AP hide caption

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Senate Foreign Relations Committee Chairman Sen. Bob Corker, R-Tenn., center, and the committee's ranking member Sen. Ben Cardin, D-Md., right, were all smiles April 14 after the committee passed an agreement on oversight of Iran negotiations. But the bill has run into some outspoken opponents in the full Senate. Andrew Harnik/AP hide caption

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Senate Minority Leader Harry Reid, D-Nev., (left) and Majority Leader Mitch McConnell, R-Ky., at a ceremony last month at the U.S. Capitol. Chip Somodevilla/Getty Images hide caption

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Vice President Biden and House Speaker John Boehner wait for President Obama's State of the Union address in front of a joint session of Congress in 2012. As vice president, Biden is also leader of the U.S. Senate, but only gets a vote when senators are evenly divided. Saul Loeb/AP hide caption

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Former Massachusetts Sen. Edward William Brooke speaks in the Rotunda on Capitol Hill in Washington, in 2009 during a ceremony where he received the Congressional Gold Medal. Brooke died on Saturday at age 95. Alex Brandon/AP hide caption

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Republican U.S. Senate candidate Dan Sullivan greets supporters on election night in Anchorage. The as-yet-undecided race between Sullivan and Democratic incumbent Sen. Mark Begich was the hottest in the state. Ted S. Warren/AP hide caption

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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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