Sam Clovis, newly appointed national co-chairman of the Trump campaign, speaks during a news conference with Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, left, ahead of a rally at Grand River Center in Dubuque, Iowa, U.S., on Tuesday, Aug. 25, 2015. President Barack Obama’s top business ambassador dismissed Trump’s call for a wall along the Mexico border, saying the U.S. is focused instead on expanding business with one of its biggest trade partners. Photographer: Daniel Acker/Bloomberg via Getty Images