Sen. Marco Rubio, Florida Republican and presidential hopeful, speaks at the Family Leadership Summit in Ames, Iowa, on July 18, 2015. (Associated Press)
New Jersey Gov. Chris Christie waves to supporters after visiting with customers at the Hickory Park Restaurant, Thursday, June 11, 2015, in Ames, Iowa. (AP Photo/Charlie Neibergall)
New Jersey Gov. Chris Christie speaks about education reform, Thursday, June 11, 2015, at Iowa State University in Ames, Iowa. (AP Photo/Charlie Neibergall)
New Jersey Gov. Chris Christie speaks about education reform, Thursday, June 11, 2015, at Iowa State University in Ames, Iowa. (AP Photo/Charlie Neibergall)