Joni Ernst

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U.S. Sen.-elect Joni Ernst speaks to supporters during an election night rally, Tuesday, Nov. 4, 2014, in West Des Moines, Iowa. Ernst defeated U.S. Rep. Bruce Braley, D-Iowa, in the race to replace retiring U.S. Sen. Tom Harkin. (AP Photo/Charlie Neibergall) **FILE**

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U.S. Sen.-elect Joni Ernst speaks to supporters during an election night rally, Tuesday, Nov. 4, 2014, in West Des Moines, Iowa. Ernst defeated U.S. Rep. Bruce Braley, D-Iowa, in the race to replace retiring U.S. Sen. Tom Harkin. (AP Photo/Charlie Neibergall)

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Republican Senate candidate State Sen. Joni Ernst casts her ballot in the general election, Tuesday, Nov. 4, 2014, in Red Oak, Iowa. Ernst is running against Democrat U.S. Rep. Bruce Braley for the U.S. Senate seat of Tom Harkin, who is not seeking reelection. (AP Photo/Charlie Neibergall)

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Republican Senate candidate State Sen. Joni Ernst casts her ballot in the general election, Tuesday, Nov. 4, 2014, in Red Oak, Iowa. Ernst is running against Democrat U.S. Rep. Bruce Braley for the U.S. Senate seat of Tom Harkin, who is not seeking reelection. (AP Photo/Charlie Neibergall)

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Republican Senate candidate Joni Ernst is pulling ahead of rival Bruce Braley in the Iowa race. (AP Photo/Nati Harnik)

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Joni Ernst for U.S. Senate capaign ad.

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Joni Ernst for U.S. Senate capaign ad.

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A political science professor at Iowa State University, said Democrats are turning to the Koch attacks in Iowa in hopes of raising questions about the trustworthiness of Republican candidate Joni Ernst. (AP Photo/The Des Moines Register, Andrea Melendez)

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Democrat Bruce L. Braley raised the specter of the Koch brothers Sunday in a debate with Republican Joni Ernst. The Iowa candidates are seeking a U.S. Senate seat. (Associated Press)

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Iowa state Sen. Joni Ernst (right), republican candidate for U.S. Senate, sparred with democratic candidate U.S. Rep. Bruce Braley on Sunday, over immigration and the definition of "amnesty." The Des Moines Register released a poll over the weekend that showed Mrs. Ernst had opened up a 6-percentage-point lead over Mr. Braley. (Associated Press)

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Joni Ernst

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Jeb Bush says he is just helping Republicans win Senate races this fall. He is crossing the country attending events for (clockwise from top right) Tom Cotton of Arkansas, Cory Gardner of Colorado, Joni Ernst of Iowa, Monica Wehby of Oregon and others. He also might be laying ground for his own White House campaign. (associated press photographs)