Senator Ted Cruz, a Republican from Texas and 2016 presidential candidate, left, and Ben Carson, 2016 Republican presidential candidate, participate in the Republican presidential debate at the Ronald Reagan Presidential Library in Simi Valley, California, U.S., on Wednesday, Sept. 16, 2015. After a friendly round of introductions, the second Republican presidential debate quickly plunged into clashes that shifted from policy to the personal, with more politically experienced insiders trying to gain an advantage against the front-runner at center stage: Donald Trump. Photographer: Max Whittaker/Pool via Bloomberg