Mr Dean's self-destruction shows that democracy works

Politics is a fragile business. One moment Howard Dean was carrying all before him, raising almost as much money as the other Democratic hopefuls put together, enthusing the party grassroots, collecting endorsements and leading his rivals in opinion polls. The next, his campaign is all but over and the clever money is on John Edwards or John Kerry to take on George Bush in November.

Coming third in the Iowa caucuses was a serious blow to the Dean candidacy but, with his neighbouring state of New Hampshire coming next, it was survivable. What has torn the heart out of his campaign was his speech to supporters after the Iowa result, in which he struck a curiously deranged note. His peroration, declaring his determination to fight on, ended on a strangled cry of defiance, a screaming "yeehah!" It reminded British viewers all too much of Neil Kinnock bouncing on to the stage at the Sheffield rally in 1992 shouting "We're all right!"

It can seem unfair that a political career should be broken on one unguarded moment, but we should welcome the brutality of democratic politics, because it is moments such as these that test the fitness of potential leaders.

A momentary lapse can destroy a politician when it taps into a deeper unease. This one clarified a growing hesitation about Mr Dean among both Democrats and the wider electorate: his initial success was built so much on the anti-Bush anger of the party faithful that there was always a doubt about whether it could be channelled in a constructive direction. That anger originated in the feeling that Mr Bush had stolen the 2000 election, and was made raw by the failure of established politicians to vent the fierce anti-war sentiments of much of the party's base.

There is, perhaps, no process of democratic selection as rough and testing as the US primaries. It was in the snows of New Hampshire, for example, that Bill Clinton faced and overcame the allegations of an affair with Gennifer Flowers. Mr Dean has stumbled at the outset. Now the fascinating question is who, out of Mr Edwards, Mr Kerry or General Wesley Clark, will emerge, and how bloodied, from the contest over the next few weeks. American politics has become interesting again.