THOMAS MITCHELL: The spreading menace of McCain-Feingold There is one law Congress, in all its collective wisdom, can never repeal: the law of unintended consequences. In a fit of pique over the huge sums it was costing them to successfully defend their coveted seats of power, Congress passed the McCain-Feingold law, setting limits on what people could spend -- and when -- exercising what had once been their free speech right to advocate candidates for federal office. Of course, before the ink was dry on the parchment, along came the 527s -- MoveOn.org, billionaire George Soros' America Coming Together and...