The Arizona senator has been a virtual one-man opposition to the president. But now his support is vital to attempts to repeal Obamacare • Mary Dejevsky is a writer and broadcasterJohn McCain was guaranteed a hero’s welcome in Washington when he returned for today’s crucial Senate vote. His disclosure, just days earlier, that he had been diagnosed with brain cancer, had prompted an outpouring of tributes to the veteran senator whose whole adult life, it sometimes seemed, had been spent ch...