NEW : Barack Obama makes fun of Hillary Clinton for drinking a shot in front of media . After a weekend of playing defense about his `` bitter '' comments , Sen. Barack Obama went on offense Monday against his Democratic rival and the presumptive Republican nominee . NEW : Clinton 's verbal attacks on Obama met with boos from audience . Comment: At fundraiser , Obama said some Pennsylvanians bitter and clinging to guns , religion .
NEW : Barack Obama makes fun of Hillary Clinton for drinking a shot in front of media . NEW : Clinton 's verbal attacks on Obama met with boos from audience . Comment: At fundraiser , Obama said some Pennsylvanians bitter and clinging to guns , religion .