It’s not unusual for a president’s party to do badly midway through his second term; the exception was 1998, when the Democrats made gains on the back of the attempt to impeach Bill Clinton. But the Republicans lost control of the Senate during Reagan’s second term in 1986, and the Democrats made huge gains in 1974, in what started as Richard Nixon’s second term, a few months after he resigned in disgrace.

So Bush Jr has conformed to the pattern. He will now be regarded as a lame-duck president, although things have been going badly for the last year anyway: the changed dynamics in Congress will be symptom as much as cause. But a Democrat majority in the House will certainly not make life any easier.

The key point to note is that at this point the 2008 presidential race is unusually open. In 1988 and 2000 there was an incumbent vice-president who was front-runner for his party’s nomination, but Dick Cheney will not be a contender in 2008. Instead the current GOP favourite is John McCain, who is loathed by much of his party’s base.

Although today’s result could have been much worse, Bush’s standing is sufficiently damaged that his endorsement will not be a major attraction for any of the Republican hopefuls. So expect the White House to become increasingly irrelevant over the next two years as the focus shifts to the manoeuvring for 2008.

On the Democrat side, Hillary Clinton is the front-runner; much of her party is deeply sceptical of her and there are serious doubts about her electability, but realistically her opponents have less than 12 months in which to rally behind an alternative.

Ultimately, this is probably the secret for the otherwise puzzling success of American democracy. The system may work not in spite of but because of its dysfunctionality: politicians who in other countries might be spending their time enacting policies and therefore screwing things up, in the US are always out running for re-election.