Next Thursday's caucuses in Iowa mark the start of the American election season. Barring a late surge by the populist John Edwards, the Democratic meetings will either give Hillary Clinton a strong chance of becoming the first woman president or Barack Obama a strong chance of becoming the first black one. A female president would be no big deal for the US, which has stood for most of its history in the world's feminist vanguard. A black president, however, would be epochal.

That Mr Obama's candidacy is even viable calls for a re-examination of America's central problem, which for generation after generation has bloodied its streets, haunted its conscience and warped its institutions. Does Senator Obama represent a "new kind of politics", as he has claimed? If so, how? And does it have anything to do with his race?