Hillary Clinton leads Barack Obama in Pennsylvania by a 52 percent to 41 percent margin, according to an American Research Group poll conducted March 7-8. The margin of error is 4 percent. This compares to the 52 percent to 37 percent margin in a Rasmussen Reports poll conducted March 5. Both show Clinton re-establishing herself in Pennsylvania compared to late February when several polls showed Obama, riding his wave of momentum, had closed the once big gap between them in that state.