Josh Bolten - White House chief of staff and official keeper of secrets for President George W Bush - told me the other day that he has bought "countdown clocks" for his desk and those of senior colleagues at the White House. They relentlessly tick off the days, hours, minutes and seconds until noon on 20 January 2009, when Bush will finally leave 1600 Pennsylvania Avenue. By my calculation, Josh's clocks will show 804 days, three hours and 45 minutes at precisely 8.15 on the morning of Wednesday 8 November.

That date is not chosen at random: for the Bush adminis tration, it will be the morning after the night before, when perhaps 125 million Americans will have cast their votes in the 2006 midterm elections and delivered their most definitive verdict yet on the 43rd US presidency. Will the Demo crats have won a landslide victory, giving them control of Congress next January for the first time in 12 years? Will that rein Bush in, or increase his boneheaded obduracy over Iraq and everything else? Will the Democrats then declare outright war on Bush in revenge for everything he's doing?

We can be certain of only one thing: the results that morning will have a profound effect on America and the world, not only for those 804 days of Bush left, but perhaps for decades to come. Besides getting ever closer to the chilling prospect of his final mad days in the bunker, we will see Republican and Democratic presidential candidates for 2008 duck and weave, changing policies and tactics as they try to fit in to the new political landscape. Iraq, Afghanistan, anti-terrorism, healthcare, the economy, social security, tax: all will be affected by what voters decide on 7 November, making this year's mid term elections the most significant in US political history.

A month ago, the outlook was of a trickle towards the Democrats; now it is a surge - propelled not just by a storm of Bush hatred that is gaining momentum, but by random events such as the pathetic "sex scandal" of the now former congressman Mark Foley. In the latest Newsweek poll, 55 per cent of likely voters say they want a Democrat-controlled Congress, com pared to just 37 per cent planning to stick with the Republicans. In the House, the Republicans hold 230 seats and the Democrats 201, while the Republicans control the Senate by 55-45. With all 435 seats in the House and 33 in the Senate up for election this year, the Democrats need to take just 15 House and six Senate seats from the Republicans.

So, yes, there could well be a landslide and the blood may start flowing between Capitol Hill and Pennsylvania Avenue. But domestic American politics and its complex, gerrymandered systems make the obstacles to change much higher: the Democrats need not just an anti-Bush storm on 7 November, but a hurricane. Those Newsweek figures may seem to clinch it, but overall the poll translates into the Democrats regaining just 17 House seats and leaving the Senate on a knife-edge.

If voting were to take place on the day I am writing this, I would predict 34 House seats and five (possibly six) in the Senate shifting to the Democrats. But hurricanes can gather momentum or they can subside to small gusts; the mood in America is so fickle that, in the few days left, either could happen. Bush and Karl Rove are said to be "upbeat" and even "fired up"; a veteran of the Reagan and first Bush administrations, meanwhile, confessed that, for the first time, "being a Republican, I could just weep right now". Polls show that 84 per cent of the US public know who poor Foley is. That is a higher recognition figure than many presidential candidates get.

Bush and Rove, however, are as ruthless and politically amoral as ever - while the Democrats remain infuriatingly feckless. There has been a stream of unparalleled fiascos: Iraq (going "remarkably well", as Dick Cheney said the other day), Afghanistan, Hurricane Katrina, Jack Abramoff, Terri Schiavo, Harriet Miers, corruption outrages (two former Republican congressmen are in jail and several more, including Bob Ney, who still sits in Congress, are heading there) and various ludicrous sex scandals. (My favourite is that of Don Sherwood, a 65-year-old, happily married father-of-three who, as a representative for Pennsylvania, stood for traditional family values. He settled with a mistress who brought a $5.5m lawsuit against him after police found her cowering in a locked bathroom in his DC flat saying he'd tried to "choke" and "strangle" her.) Yet, instead of just giving up the ghost, Bush and Rove and their cronies are coming out fighting, furiously spending money and smearing away as only they know how.

Their initial plan was to resort to the tactic that has brought them unfailing success since the 11 September 2001 atrocities: engender fear. In a series of speeches that began immediately after Labor Day (4 September), Bush hammered away at the theme that Americans should feel very, very, very scared - and that only he and the Republicans could protect them. The Republicans duly came out with a 2006 advert reminiscent of Lyndon B Johnson's infamous 1964 Daisy ad against Barry Goldwater, openly suggesting that the Democrats are somehow allied with Osama Bin Laden.

Initially, Rove's strategy worked like wizardry and Bush's approval ratings climbed several points. But with US casualties in Iraq mounting - October will be the worst month for military deaths since the war began - and Americans at last beginning to realise that Iraq is not actually linked to the "war against terror", the magic started to evaporate. Establishment and decent old Republican loyalists such as 79-year-old John Warner, chairman of the Senate armed services committee (yes, the one who was once married to Elizabeth Taylor) publicly started to abandon Bush on Iraq.

"We will stay the course until the job is done," is thus a mantra suddenly heard much less often here (though nobody seems to have told Tony Blair). In the words of Bill Clinton, the fear-mongering tactic has become "kind of a mangy old dog they're running out of the kennel one more time, and I don't think it'll hunt". Congressman Harold Ford, who is running neck-and-neck for Bill Frist's old Senate seat in Tennessee, actually dared to come out with an advert saying specifically that America should not now stay the course.

Playboy racism

Morally flexible as ever, Bush and the Republicans switched tack to another tried and tested formula: that the Democrats would, in Bush's words a few days ago, "raise your taxes and figure out new ways to spend your money".

In a subtly racist and peculiarly nasty tactic, the GOP is now singling out Charlie Rangel of New York, who would become chairman of the House ways and means committee, which writes tax laws, if the Democrats take the House. That he is a 76-year-old black man who represents a poor part of Harlem is never expressly mentioned, but the message is not in doubt. Ford is also black, but his Republican opponent, Bob Corker - who is worth at least $200m - is portraying Ford as a spoiled rich kid. Referring to the presence of 36-year-old, unmarried Ford at a Playboy party, a voice in a Corker ad intones: "What kind of man parties with Playmates in lingerie, then films political ads from a church pew?" The racism is predictable: there are more black candidates running for the Senate or in the 36 governorship elections than ever before.

Sexism is now a constant presence, too. The Republicans evoke the terrible spectre of Representative Nancy Pelosi becoming Speaker - second in line to the presidency after Vice-President Cheney. In Missouri, another of the states in the balance, an ad for the 50-year-old incumbent senator, Jim Talent, says his Democratic opponent, Claire McCaskill, aged 53, is a "liar" who will not hesitate "to cheat" to get elected. Women, I should point out, still have much less equality in US politics than they do in Britain.

We have reached the stage when personalities begin to subsume issues. Rick O'Donnell of Colorado, a hapless 36-year-old Republican, has his Democratic opponent gleefully airing ads showing O'Donnell grinning on the steps of Air Force One next to Bush - footage congressional candidates would normally kill for - with a voice gloomily intoning: "Another vote for George Bush's agenda." For most Republican candidates, the president is a liability.

Rigged machines

The issues that most concern Americans - which an AP/Ipsos poll found were, in order of precedence: Iraq, the economy, terrorism, healthcare, social security, political corruption, taxation, petrol prices, immigration and same-sex marriage - are, as a result, featuring less in media coverage. A study in 36 Midwest states by the University of Wisconsin found that TV stations are devoting 36 seconds of their evening news bulletins to the elections, and more than three-quarters of the coverage was about personalities rather than issues. A similar study spanning 9-13 October, by the Tyndall Report, found that the networks devoted 13 minutes on average to Foley's ridiculous IM-ing - and just six to the elections themselves.

If the Democrats win control of the House, the party leadership will not, contrary to rumours, impeach Bush over Iraq. Rather, it will introduce a torrent of legislation - to raise the minimum age, make it legal for the government to negotiate Medicare prescription prices with drug companies, revitalise student loans, fund stem-cell research, implement recommendations of the 9/11 Commission, and so on - which Bush, in due course, will veto without hesitation.

Bloody trench warfare would break out unless Bush suddenly switched personalities in the way Arnold Schwarze negger of California has managed to do in less than a year; the Governor Terminator of 2005 has transformed into a warm-and-fuzzy, environment-loving candidate for re-election in 2006 who, consequently, will romp back to power in Sacramento. I can't see Bush evolving a similar persona: from the time he retreated into alcoholism in his twenties, he has been frantically avoiding introspection or inconvenient realities.

More worrying than trench warfare, for Bush's crowd, is the prospect of victorious Democrats exercising the right to subpoena government documents. Who, they might ask, were the members of Cheney's top-secret "energy task force"? Perhaps the late Ken Lay, Enron's mega-crook? How many times did Abramoff visit the White House, and why? What did he discuss in meetings with Rove? (Or will the documents have been shredded and tapes mysteriously wiped?)

All this assumes that the elections are fair and honest. It is conceivable that Diebold voting machines were tampered with to bring Bush victory in 2004, which would explain why exit polls predicted victory for John Kerry: they were right.

A study published last month by Princeton University has concluded that Diebold's AccuVote-TS and AccuVote-TSx machines - which will count at least 10 per cent of the nation's votes - can be infected, in less than a minute and "with little risk of detection", with a virus designed to favour one candidate.

But take heart; while you have been reading this, those White House countdown clocks have been ticking away. In 2009 they will at last reach the long-awaited target of 000:00:00:00, and the presidency of George W Bush will finally become a fast-receding nightmare.

The midterms by numbers
Research by Anthony Lane

62% George Bush's approval rating during the 2002 midterm polls

37% Bush's current approval rating

41% Bill Clinton's approval rating in 1994, when the Republicans swept to power in Congress

80% Voters who will use touch-screen voting machines in this year's election

27 number of states that don't provide a paper trail to support touch-screen voting machines