Sen. Ted Cruz prays before the start of his Religious Liberty Rally last weekend in Des Moines, Iowa. The event was part of Cruz's push to energize evangelical voters. Scott Olson/Getty Images hide caption

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Republican presidential candidate Donald Trump speaks at a press conference Wednesday prior to a town hall meeting at Pinkerton Academy in Derry, N.H. Matthew Healey/UPI/Landov hide caption

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Republican presidential candidate and Wisconsin Gov. Scott Walker speaks at the Iowa State Fair, where he encountered protesters over his record in Wisconsin. Charlie Neibergall/AP hide caption

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Democratic presidential candidate Hillary Clinton speaks at the Iowa Democratic Wing Ding on Friday in Clear Lake, Iowa. Win McNamee/Getty Images hide caption

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In 2007, then-candidate Barack Obama rode bumper cars at the Iowa State Fair with his daughter Sasha. M. Spencer Green/AP hide caption

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