BOSTON – In an epic upset in liberal Massachusetts, Republican Scott Brown rode a wave of voter anger to defeat Democrat Martha Coakley in a U.S. Senate election Tuesday that left President Barack Obama's health care overhaul in doubt and marred the end of his first year in office. The loss by the once-favored Coakley for the seat that the late Sen. Edward M. Kennedy held for nearly half a century signaled big political problems for the president's party this fall when House, Senate and gubernatorial candidates are on the ballot nationwide.