When Winston Churchill was at the nadir of his career, he wrote a biography of his ancestor, the Duke of Marlborough. In his wilderness years he needed to be reminded that even the greatest men of destiny go through periods when it all seems pretty hopeless. ‘Every taunt, however bitter; every tale, however petty; every charge, however shameful, for which the incidents of a long career could afford a pretext, has been levelled against him,’ Churchill wrote.