Mr Obama's victory this week was no less astonishing for the fact that it was widely predicted by the opinion polls. Everywhere, we have heard the sound of doors slamming on the past; on the bitter legacies of slavery and segregation; on a Republican ascendancy born of the struggle over civil rights and Vietnam; on the Reagan era of unfettered markets; and on the world's deepening disenchantment with Washington.

There are caveats, of course. It should be obvious to all that expectations of Mr Obama are impossibly high. Even so singular a politician will struggle to make the transition from the soaring poetry of the campaign to the workaday prose of government.

Rhetoric will not fix the US economy; or save the planet from climate change. Eloquence will not get US troops out of Iraq; or the Taliban out of Afghanistan. For all that, the simple fact of Mr Obama's victory has changed the geopolitical game.