U.S. Republican Ben Carson's 2016 presidential bid was thrown into chaos on Thursday when his campaign manager and some 20 other staff members quit amid infighting, dropping poll numbers and negative media coverage. Barry Bennett, who oversaw Carson's rapid rise to the top tier of Republican contenders and his later fall, said he quit over differences with another top adviser to Carson, Armstrong Williams. Specifically, Bennett blamed Williams for an interview Carson gave last week to The Washington Post suggesting that the campaign was in disarray. "It's one of the stupidest things I've ever seen a candidate do," Bennett said....