Four of the contenders vying against Donald Trump for the GOP presidential nomination met onstage in Tuscaloosa, Ala., Wednesday night. Former U.N. ambassador Nikki Haley, Florida Gov. Ron DeSantis, former New Jersey governor Chris Christie and tech entrepreneur Vivek Ramaswamy faced off as the window narrows to catch up with Trump less than six weeks before the Iowa caucuses kick off the nominating contest.