Dean becomes an also-ran as Kerry forges ahead in Missouri and Arizona

Buoyed by his back-to-back successes in Iowa and New Hampshire, John Kerry has moved into big leads in two of the four most important states which vote next Tuesday, and is running a strong second in the other two.

A survey by Reuters/MSNBC/Zogby gives the Massachusetts senator a 34-point lead in Missouri over Senator John Edwards of North Carolina, the only other candidate in double figures. In Arizona, Mr Kerry leads the retired general, Wesley Clark, by 38 per cent to 17 per cent. In South Carolina, a state Mr Edwards has said he must win to stay in the contest, he holds a statistically meaningless edge with 25 per cent to Mr Kerry's 24 per cent. General Clark leads Mr Kerry by 27 per cent to 19 per cent in Oklahoma, with Mr Edwards on their heels at 17 per cent.

The poll shows how the battle for the Democratic nomination has been turned upside down by the results in New Hampshire and Iowa. The former front-runner, Howard Dean, has been transformed, for the time being, into an also-ran. Financial difficulties have forced him to drop television advertising in all seven states holding primaries on 3 February. He is running either third or fourth in Missouri, Oklahoma, Arizona and South Carolina, and is unlikely to be faring much better in Delaware, North Dakota and New Mexico.

In essence, Mr Kerry and Mr Dean have changed places since Iowa and New Hampshire. Mr Dean has seen huge leads evaporate across the country; Mr Kerry, who a month ago was languishing where Mr Dean is today, has shot to the front.

Victories of the size indicated by the polls would demonstrate that Mr Kerry's appeal stretches well beyond his native north-east, and that Democratic voters are undeterred by such labels as "Massachusetts liberal" if they are to believe, as they now seem to, that he is the candidate with the best chance of beating President George Bush.