Thom Tillis

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FILE - In this April 23, 2014, file photo, Republican senatorial candidate Thom Tillis responds during a televised debate at WRAL television studios in Raleigh, N.C. The struggle for control of the Republican Party is getting an early voter test in North Carolina, where former presidential nominee Mitt Romney and tea party favorite Rand Paul on Monday, May 5 pushed their own candidates for the right to challenge Democratic Sen. Kay Hagan in November.(AP Photo/Gerry Broome, Pool)

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Republican senatorial candidate Thom Tillis, front-runner in North Carolina's primary, may face a runoff election in July that could impede his Senate bid. (Associated Press)

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** FILE ** In this April 23, 2014, photo, Republican senatorial candidate Thom Tillis responds during a televised debate at WRAL television studios in Raleigh, N.C. (AP Photo/Gerry Broome, Pool)

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Republican senatorial candidates from left, Greg Brannon, Heather Grant, Mark Harris and Thom Tillis wait to participate in a televised debate at UNC-TV in Research Triangle Park, N.C., Monday, April 28, 2014. (AP Photo/ Pool)

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Republican senatorial candidates Thom Tillis responds during a televised debate at UNC-TV in Research Triangle Park, N.C., Monday, April 28, 2014. (AP Photo/ Pool)