Des Moines

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Sen. Lindsey Graham, R-S.C., speaks during the Iowa Republican Party's Lincoln Dinner, Saturday, May 16, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) ** FILE **

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Donald Trump speaks during the Iowa Republican Party's Lincoln Dinner, Saturday, May 16, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) ** FILE **

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Former New York Gov. George Pataki speaks during the Iowa Republican Party's Lincoln Dinner, Saturday, May 16, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)

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Louisiana Gov. Bobby Jindal speaks during the Iowa Republican Party's Lincoln Dinner, Saturday, May 16, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)

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Democratic presidential candidate Hillary Rodham Clinton poses for a photo with Simpson College student MacKenzie Bills, center, after meeting with Iowa Democratic Party lawmakers at the Statehouse, Wednesday, April 15, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)

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Democratic presidential candidate Hillary Rodham Clinton held a small-business roundtable Wednesday in Des Moines, Iowa, as part of her effort to show her more personal side, even as she eased away from President Obama's policies. (Associated Press) ** FILE **

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Democratic presidential candidate Hillary Rodham Clinton waves as she arrives at the Iowa Statehouse to meet with Democratic Party lawmakers, Wednesday, April 15, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) ** FILE **

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Wisconsin Gov. Scott Walker speaks during the Iowa Agriculture Summit in Des Moines, Iowa, on March 7, 2015. (Associated Press) **FILE**

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Former technology executive Carly Fiorina speaks during the Freedom Summit, in Des Moines, Iowa, on Jan. 24, 2015. (Associated Press) **FILE**

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Wisconsin Gov. Scott Walker speaks during the Iowa Agriculture Summit in Des Moines, Iowa, in this March 7, 2015, file photo. (AP Photo/Charlie Neibergall) ** FILE **

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Wisconsin Gov. Scott Walker speaks during the Iowa Agriculture Summit, Saturday, March 7, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)

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Former New York Gov. George Pataki speaks during the Iowa Agriculture Summit, Saturday, March 7, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)

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Sen. Ted Cruz, R-Texas, speaks during the Iowa Agriculture Summit, Saturday, March 7, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) ** FILE **