Scott Walker, governor of Wisconsin, speaks during the Iowa Ag Summit at the Iowa State Fairgrounds in Des Moines, Iowa, U.S., on Saturday, March 7, 2015. The event aims to highlight the role that agriculture plays in Iowa and the rest of the world. Photographer: Daniel Acker/Bloomberg via Getty Images

Scott Walker, governor of Wisconsin, speaks during the Iowa Ag Summit at the Iowa State Fairgrounds in Des Moines, Iowa, U.S., on Saturday, March 7, 2015. The event aims to highlight the role that agriculture plays in Iowa and the rest of the world. Photographer: Daniel Acker/Bloomberg via Getty Images