The debates are over, and with just 18 days to go until America chooses a president, it is still too close to call. Nick Morrison looks at the race for the White House - and what the outcome will mean for Britain.

FOUR years ago it came down to some hanging chads - the circles of paper left as voters punched holes in their ballot forms - but this year it may not even be a paper width which separates the candidates. With just over two weeks left, and after a long and gruelling campaign, the polls are showing incumbent George Bush and challenger John Kerry neck and neck.

It was a very different picture at the beginning of the month. Then, it was the President's to lose, as he led by up to 12 points - Republican attacks on their "flip-flopping" opponent appeared to have hit home and the Democrat campaign struggled to find a coherent message.

But any doubts over whether the televised debates can affect the outcome have been dispelled by the events of the last ten days. Bush scowled his way through the first debate. His nervous laughter before answering questions, reluctance to deviate from his few well-worn slogans and stumbling over words - even raising a giggle when he talked of the "Internets" - hardly inspired confidence in the Commander-in-Chief.

He may have recovered in the two subsequent face-offs, although they were both generally scored as Kerry victories, but by then the challenger was back in the race.

But what marks this presidential campaign out from many of its forerunners is not in the closeness of the race, but in the divisions it has exposed; divisions which exist not just between the two candidates, but stretch deep into society.

"In every presidential election there is a lot of sound and fury, but there are divides there in the politics that are very difficult to bridge," says Rod Hague, retired senior politics lecturer at Newcastle University.

"These kinds of cultural, value and lifestyle issues, point to differences of belief and conviction which it is hard to fudge over, and here politics is reflecting what has been going on inside society."

Hence, alongside Iraq, the war on terror and the economy, key issues in this campaign are abortion, gay marriage and research using stem cells taken from human embryos.

Their prominence is a result of the rise of the Christian right, the major political development of the last 20 years, and a reaction to the liberalisation of the 1960s and 70s, when abortion, gay rights and women's rights came to the fore.

This is a constituency which has been assiduously courted by Bush - earlier this year he proposed an amendment to the constitution to ban gay marriage - and marks a sharp difference from his father, a one-term president.

"The Christian right has got an arm-lock on the Republican Party. Half a century ago it was a very different party, and that is reflected in the temperaments of the two Bushes," says Mr Hague.

"Bush senior was a traditional Republican, more towards the liberal wing of his party, whereas his son has been reared in a very different party of conservative fundamentalism. He is a different kettle of fish ideologically and even culturally from his father.

"He committed himself to the Christian right to win the Republican nomination and the presidency, and while I would not say it has governed his actions, it has certainly been his power base."

The religious vote is a key constituency for both candidates, and this week's pronouncement by Roman Catholic bishops that voting for Kerry would be a sin is potentially crucial in a country where a quarter of the population are Catholic.

But many commentators see Bush's hard-line stance as preaching to the converted and instead point to his repeated efforts to paint his opponent as a liberal, generally considered a term of abuse in America, as the most profitable line of attack.

The Bush camp will also want to keep the war on terror uppermost in the electorate's minds on November 2, with their candidate painted as a firm and decisive leader, in contrast with Senator Kerry, who at first supported the invasion of Iraq, before seizing upon it as a chance to attack the incumbent.

But although the war on terror may benefit Bush, continued turmoil in Iraq, and the Abu Ghraib prison scandal, are seen as fruitful issues for Kerry, who will also emphasise America's economic difficulties, with Bush expected to be the first president since Herbert Hoover 72 years ago to see a net loss of jobs on his watch.

And now, with just 18 days left, the campaign will move to the key swing states which will decide the result of the election. The electoral college system, which gives each state a certain number of votes depending on population, means the candidates will now focus on the battleground states, numbering from three to 20, depending on the pollster.

Four years ago, it may have been Florida which kept the nation waiting, but had Al Gore won his home state of Tennessee, he would be the one now seeking re-election. Florida, Ohio and Pennsylvania have the most electoral votes on offer among the undecided states, but Michigan, Minnesota, Arkansas and Wisconsin are among those that could go either way, and it is in these states that the influence of third candidate Ralph Nader could prove decisive.

Although Nader will pick up just one or two per cent of the vote, that most of it is likely to come from those who would otherwise vote Democrat may hurt Kerry.

"The race is very tight and it is going to go right down to the wire. It will depend on the success of mobilising the vote in the battleground states," says Rod Hague.

But while deep divisions exist between the two candidates, the implications for the rest of the world may not be as stark as they at first appear. Although Kerry has been critical of the president over Iraq and would be expected to take a more measured approach to foreign policy, America has always reserved the right to take unilateral action, whichever party controls the White House.

The Democrats may traditionally have preferred to work through international organisations, but the Clinton administration was not adverse to flexing American military power, albeit as a last resort.

Where there may be a ripple from a change at the top is in the position of Tony Blair. A Bush defeat will leave the Prime Minister embarrassingly exposed as virtually the solitary pro-war voice, an apologist who refuses to apologise. But this is unlikely to prove an insurmountable hurdle.

"Tony Blair has clearly bent over backwards to be Bush's best buddy, at tremendous political cost, and I think if Kerry wins relations will be a little bit cool for a while," says Mr Hague.

"But there is slightly more ideological affinity between Blair and Kerry than between Blair and Bush, so I suspect there are Labour Party observers already making efforts to build bridges with a possible Kerry administration. After all, Blair was Clinton's best buddy as well."