The historical analogies for the phenomenon that is Barack Obama have already stretched credibility. For a while pundits likened him to the effete loser Adlai Stevenson, the Democratic party’s 1950s version of Labour’s Hugh Gaitskell, the greatest prime minister we never had. But Obama doesn’t seem like such an airhead after his gritty, crushing defeat of Hillary Clinton in Iowa. I long thought he’d win; but I never thought it would be by eight points, or that he’d push Clinton into third place. So now the favourite analogy is JFK: the young, hopeful rhetorician urging a New Frontier after two...