People, on the other hand, are anything but straightforward. They dissemble, evade and lie - even to themselves. They confuse what they want to be true with what they know to be true. A person who does not contradict himself or herself is a bore, an ideologue or both. To fit people into a bigger picture, you must first change their shape.

With just one week to go before the midterm elections, the polls speak with one voice. The Republicans are heading for resounding defeat. A Pew research poll released late last week shows the Democrats with a double-digit lead among likely voters in the crucial competitive districts. The Democrats need 15 seats to retake the House of Representatives and six to win the Senate.

In the 131 House seats where John Kerry mustered only 40-49% of the vote two years ago, Democrats now have a lead of about 5%. They are ahead among men, whites, suburbanites, southerners and rural voters, all groups in which they trailed heavily in 2004. Independents now favour Democrats by 16%; four years ago it was just 3%.

The Republicans are favoured for dealing with terrorism, North Korea and immigration. On everything else, including Iraq, the economy, healthcare, morality and taxes, the Democrats are ahead. Even the Republicans' most faithful supporters are rapidly losing confidence in the administration's strategy on Iraq. Almost half of white evangelical Protestants believe the US should set a timetable for withdrawal - a 40% hike in just two months.

If the pollsters are correct, the US is set for a transformation on a scale somewhere between the Gingrich revolution of 1994, the last Republican legislative revival, and the Blair landslide of 1997. Republicans are about to be crushed by a series of meteorological metaphors - tsunamis, floods and hurricanes are poised to descend on the US electoral landscape with devastating effect.

But, to hear the people talk, you would think the country was in store for little more than grey skies with a chance of rain. Many voters in key districts in the midwest say they are undecided or just plain uninterested. Ask them what will swing it for them and they shrug. The big issues, they say, are Iraq and something else - usually healthcare, the economy or social security. Hurricane Katrina, corruption and terrorism never come up. They will answer questions about the election if you ask them, but it rarely seems to have been on their minds before you interrupted. Even big regional papers, such as the Chicago Tribune, are more focused on the races for local and state office (if indeed they are looking at politics at all) than the national scene. The issues people say are important are national but for the most part the voters insist on a local remedy. "I'll vote for the man not the party," they say. And which man do they like best? They're not sure.

Take Barbara, a "staunch Democrat", who lives in Chicago's suburbs, in one of the most hotly contested districts in the country, and voted for Bush in 2000. She is opposed to the war, but she is not yet sure whether she will vote for Democratic candidate Tammy Duckworth, the Iraq war veteran who lost her leg in the conflict. "I don't have any real feelings about her one way or another," she says. What will swing it for Barbara? "I don't know. Something will hit me."

The Democrats do seem more determined; those who voted for Bush in the last election are having second thoughts about both him and his party. But you come away with a sense that this could end up resembling Kerry's defeat in 2004 or John Major's victory in 1992.

None the less, two common strands do tie the people and the polls. First, the American public has concluded that the Iraq war has been an abject failure and wants the troops to come home. In 1999, George Bush Sr explained why he didn't move on to Baghdad after the first Gulf war. "Whose life would be on my hands as the commander-in-chief because I, unilaterally, went beyond international law, went beyond the stated mission and said, 'We're going to show our macho? We're going to be into Baghdad. We're going to be an occupying power - America in an Arab land - with no allies at our side.' It would have been disastrous."

This accurately describes his son's actions and, more importantly, the way they are commonly understood. The principle determinant of American support for any military intervention is not whether it is right or wrong but whether people think it will be successful.

For the past three years Bush has been telling anyone who would listen that the only option was to "stay the course". So long as people thought things were going well, they backed him. With US casualties rising and talk of civil war no longer taboo, the mood has soured. Last week he said that staying the course had never been his strategy. He refused to set a timetable but instead referred to "benchmarks". This may be one semantic illusion too many. They now fear that, having lied his way into it, he will lie his way out of it.

The second is that, largely as a result of the war, Bush has become a political liability. Attempts to pass this off as midterm blues simply do not wash. Six years into Clinton's presidency in 1998 - after the Lewinsky scandal had broken - the Democrats picked up five seats. In Reagan's sixth year, Republicans once again lost just five.

In 2004 Bush stood not for president but for commander-in-chief - the war leader. He called himself "the decider" - a man of principle and determination who checked his gut before he checked the polls. Unlike Kerry, the "flip-flopper", he would stand his ground when times were hard.

"The greatest thing about this man is he's steady," said comedian Stephen Colbert in a now famous parody before the White House correspondents' dinner in May. "You know where he stands. He believes the same thing on Wednesday that he believed on Monday, no matter what happened Tuesday. Events can change; this man's beliefs never will."

With Bush's approval ratings stuck in the high 30s and low 40s since Katrina, Democrats run ads tarring their opponents by association with the president. One ad in Colorado shows Republican Rick O'Donnell standing alongside Bush, and warns that a vote for O'Donnell means "another vote for George Bush's agenda". Meanwhile, many Republicans are desperate to distance themselves from him. "George Bush is not a message I want to talk about," struggling Indiana congressman John Hostettler told the Chicago Tribune recently.

Quite what impact this will have on the elections on November 7 is not quite clear. Bush isn't on the ballot and the House of Representatives could not recall the troops even if it wanted to. The fact that Americans want to change course at home as well as abroad does not mean that they want to follow the Democratic course - even if they knew what it was. People are complicated. And the only poll that matters has not yet taken place.

g.younge@theguardian.com