John Thune

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Senate Minority Leader Mitch McConnell of Ky., followed by Sen. Roy Blunt, R-Mo., left, and Sen. John Thune, R-S.D., arrives for a news conference on Capitol Hill in Washington, Tuesday, Feb. 4, 2014, after their weekly policy luncheon. (AP Photo/Charles Dharapak)

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Sen. John Thune

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**FILE** With fellow Republican Sen. John Thune of South Dakota (left) and others looking on, Senate Minority Leader Mitch McConnell of Kentucky outlines Republicans' stance on negotiations with the president and Hill Democrats on the "fiscal cliff" on Nov. 27, 2012. (Associated Press)

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Republican presidential candidate Mitt Romney, with Sen. John Thune of South Dakota, speaks Wednesday to workers at Nationwide Insurance Co. in Des Moines, Iowa. Mr. Romney is using a tough stance against illegal immigration to separate himself from his rivals for the nomination. (Associated Press)

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Sen. John Thune, R-S.D., along with GOP leadership, speaks to the media after the Senate passed the debt ceiling plan, on Capitol Hill, in Washington, D.C., Tuesday, Aug. 2, 2011. (Drew Angerer/The Washington Times)

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Sen. John Thune of South Dakota has declined to pursue a presidential bid next year and will remain in the Senate where he's serving his second term. (Associated Press)