A top Obama administration lawyer defending last year's healthcare law ran into skeptical questions Wednesday from three federal judges here, who suggested they may be ready to declare all or part of the law unconstitutional. And in an ominous sign for the administration, the judges opened the arguments by saying they knew of no case in American history where the courts had upheld the government's power to force someone to buy a product. "I can't find any case like this," said Chief Judge Joel Dubina of the 11th Circuit Court of Appeals. "If we uphold this, are there any limits"...