PUNDITS predict that the Republicans will be swept from power on Capitol Hill on November 7 by an elemental force of voter anger aimed at President Bush and Congress. Some are forecasting a “Democrat tsunami”, while Charlie Cook, the pre-eminent American election guru, talks of a “Category 5 hurricane”.

But Democrats have learnt from bitter experience that breaching the Republican defences — even with an opinion poll yesterday showing them with a 14 per cent lead nationally — is harder than it looks. The more fatalistic among them point out that in the year since the Katrina disaster the US has received many warnings about other hurricanes heading towards it. All of these, without exception, have fizzled out into nothing more severe than storms.

At the Democratic Congressional Campaign Committee headquarters, Karin Johanson, the executive director, has taken up smoking again, but with only eight days to go before polling day she says that there is scant time for indulging the habit.

Speaking to The Times as she pored over the latest numbers from swing seats, Ms Johanson said: “Some of the polls are looking great — really great — but some of the recent ones have been looking not so good.” The Democrats were “swimming upstream”, she said, against long-term disadvantages. They will be outspent by as much as $100 million (£52 million) in the coming week because their opponents have amassed vast war chests for TV advertising. Boundary changes (a more pejorative word might be “gerrymandering”) mean that there are far fewer marginal seats to target than there were when the Republicans took control of the House of Representatives 12 years ago.

Then there is the Republicans’ edge in identifying and mobilising supporters — the “Voter Vault” system and the “72-hour project” — which was worth perhaps an extra million votes to them in key districts two years ago. Ms Johanson said that the Democrats had improved their own “Get-Out-The-Vote” operation, although no one knows by how much.

“The Republicans have convinced everyone, not least themselves, that the reason they did so well in 2004 was because of their turnout operation,” she said. “They think they’re smarter than us, and, the truth is, some of us think they’re smarter than us.”

The Democrats need 15 net gains to regain control of the 435-member House for the first time since 1994. They can count on perhaps a dozen, but others are too close to call and the residual power of incumbency may be critical.

For instance, Tom Reynolds, who represents an endangered Republican district in upstate New York, was recently able to negotiate millions of dollars in federal aid for a snowstorm clear-up after being visited by Karl Rove, the senior adviser to the President. Polls indicate that Mr Reynolds is narrowly back in the lead.

Regaining control of the more powerful Senate is an even harder task for the Democrats, who must make six net gains from 33 seats being contested. Of these, only 15 are held by the Republicans, while at least one seat that the Democrats are defending — New Jersey — could yet be lost.

But Charles Schumer, the campaign chief of the Senate Democrats, said that in his party’s best-case scenario it would ride “a huge tsunami” on election day, winning eight seats, including even the seemingly untouchable Arizona.

Democrats have become so used to losing that most feel deeply uncomfortable about any such display of bravado. Ms Johanson said: “I worry — I'm paid to worry.”

The hurricane season is coming to an end. Instead, families are preparing for Halloween tomorrow night. And the Democrats are spooked.

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