WASHINGTON — I am rounding the last turn of Charles Moore’s magisterial biography of Margaret Thatcher. It is no sprint. It is not even a long-distance race. It is a marathon of a literary work, three volumes. Three thick volumes. Yet, as I have said, it is a masterpiece. Charles loves Ms. Thatcher. That is not to say he lets her off easy. Charles is too fine a biographer for that, and Thatcher…