MIAMI (Reuters) – A Florida judge could on Monday become the second judge to declare President Barack Obama's healthcare reform law unconstitutional, in the biggest legal challenge yet to federal authority to enact the law. The judge, Roger Vinson of the U.S. District Court in Pensacola, Florida, was expected to rule on a lawsuit brought by governors and attorneys general from 26 U.S. states, almost all of whom are Republicans. Obama is a Democrat. The plaintiffs represent more than half the U.S. states, so the Pensacola case has more prominence than some two dozen lawsuits filed in federal courts over...