(AP) - Newt Gingrich stormed to an upset win in the South Carolina primary Saturday night, dealing a sharp setback to Mitt Romney and scrambling the race for the Republican presidential nomination. Former Pennsylvania Sen. Rick Santorum and Texas Rep. Ron Paul trailed badly. Exit polling showed the former House speaker leading by a wide margin among the state's heavy population of conservatives, tea party supporters and born-again Christians. For the first time all year, Romney trailed among voters who said they cared most about picking a candidate who could defeat President Barack Obama this fall. Gingrich was ahead of the field for those voters' support. Within minutes, Gingrich summoned supporters to help him in the next-up Jan. 31 primary in Florida. "Thank you, South Carolina! Help me deliver the knockout punch in Florida. Join our Moneybomb and donate now," he tweeted.