Ben Carson, retired neurosurgeon and 2016 Republican presidential candidate, speaks during a town hall meeting at Nashua Community College in Nashua, New Hampshire, U.S., on Sunday, Dec. 20, 2015. In a grim, gloomy Republican presidential debate last Tuesday dominated by the terrorist attacks in Paris and San Bernardino, California, the candidates tried to one-up each other on who is tougher. Photographer: Andrew Harrer/Bloomberg via Getty Images