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 **
Donald Trump speaks during the Iowa Republican Party's Lincoln Dinner, Saturday, May 16, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall) ** FILE **
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)
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)
Iowa Republican Party members listen during a Jan. 10, 2015, meeting at the party headquarters in Des Moines to discuss whether the state party should carry on with a presidential straw poll. Despite criticism from some prominent Republicans, the Republican Party of Iowa's central committee unanimously voted to keep the event going. (Associated Press/The Des Moines Register, Charlie Litchfield) **FILE**
** FILE ** In this April 11, 2014, file photo, Iowa Senate candidate Joni Ernst speaks during the Iowa Republican Party's annual Lincoln Day dinner in Cedar Rapids, Iowa. (AP Photo/Charlie Neibergall, File)