On November 2, 1920, nine days before her wedding, my mother voted in the US election in which American women first had the vote. She voted for the Democratic ticket of James Cox, and a young man called Franklin Roosevelt. The Republicans won the election, putting Warren Harding into the White House.

I grew up in England, but with a lively inherited interest in US politics. This US election will be the 21st of my lifetime, the 19th I can remember, and the 15th I shall have written about as a journalist. Every one has been important; every one has taught a lesson; every one has been different.

One could add that almost every US election somewhere involves the issue of race. In 1920 a circular distributed by a racist academic alleged that Harding had a black ancestor; racial prejudice is nothing new, nor is hostile propaganda. Blogs may be a new way of spreading smears, but personal attacks go back to the origins of democratic politics.

This election is one of the most clearly divided on cultural grounds. Now that the nominations have been made, we see that the parties have chosen on the basis of cultural appeal and identification. The election is a clash of different cultures. Most voters are influenced by cultural identification. That is natural enough, although it need not degenerate into a cultural war. Yet it is surprising that the present campaign is almost overlooking very serious economic and foreign policy issues, in favour of these differences.

This probably favours the Republicans. If this were a debate on the policies of the outgoing Administration, Republican polling figures might be down with President Bush's approval ratings, which are stuck somewhere around 30 per cent. John McCain was expected to carry Mr Bush's record on his shoulders, but has skilfully freed himself from most of the burdens of the Bush years.

Barack Obama has two separate cultural identities, derived from his black father and his Harvard education. Both bring him votes, and both cost him votes. He handles the issues of race with great skill and self-assurance. He has a sympathy and thoughtfulness about race that is inspiring. Whenever he discusses these issues, one can feel that his handling of them would alone justify his being elected. A black President of his quality would be a real gift from the American people to their own social harmony.

The tone of elitism associated with Harvard has proved more difficult. Having been educated at Balliol College, Oxford, I know that I may have irritated my contemporaries with some of the qualities that can make Harvard men annoying to American voters. The phrase “effortless superiority” was first applied to Balliol, but it might just as well have been applied to Harvard.

When I listen to Mr Obama speaking, I am reminded of two other eloquent and iconic politicians that I admired, Adlai Stevenson and Roy Jenkins. The problem is that Stevenson never became President, nor Jenkins Prime Minister. American voters tend to be suspicious of intellectuals; the higher the intellect, the greater the suspicion.

Yet the Governor of Alaska, Sarah Palin, is at least as much an icon in her own culture. She calls herself a “hockey mom”, which is a clever piece of self-definition. She is a woman of the frontier, which identifies her with one of the great American myths, as well as with the slow but inevitable movement of women towards the White House. She is a white evangelical, which identifies her with a dominant voting community. It was Richard Nixon in 1968 who developed the so-called “southern strategy”. The Republicans have won the presidency seven times since 1968, to three wins for the Democrats, by mobilising this coalition of white Protestant voters.

Mrs Palin is the chief icon for this campaign, more so than Mr McCain, more than President Bush ever has been, much more than Richard Nixon, almost as much as Ronald Reagan. But this, too, can have its dangers. The average American voter may feel closest to Mrs Palin, but most American women know their own limitations. Not every white evangelical housewife wants to put another white evangelical housewife into the White House. If they do not think the candidate can do the job, they will not vote for her.

Mr McCain himself belongs to the American military tradition of public duty. If George Washington had a vote, he would vote for Mr McCain, but modern America does not breed many Washingtons. Joe Biden is another stereotype, of the Irish-American politician. Apart from Teddy Kennedy, that is not a powerful interest group nowadays.

We have only seen the start of the campaign; the candidates are still to be tested. Mrs Palin undoubtedly has a strong character, but she is also a prime target for the Democrats. If they can undermine her, or persuade voters that she is too inexperienced for the job, then the Republican story might unravel, and the Obama campaign might cruise to victory. The Republicans are uncomfortably dependent on Mrs Palin's performance.

The last two presidential elections have been very close. In 2000 and 2004, the race was too close to call at this stage of the campaign, and remained so until polling day. Everything again depends on the swing states. Their polling figures are again very close.

Between them, four medium-sized swing states in the North East and Midwest have 78 votes in the Electoral College, enough to be decisive. The polls show Mr Obama ahead by 0.3 per cent in New Hampshire, behind by 0.6 per cent in Ohio, ahead by 4.3 per cent in Michigan and ahead by 5.0 per cent in Pennsylvania. These are very narrow margins.

We do not yet know how Mrs Palin will play in New Hampshire, Ohio, Michigan or Pennsylvania. That could decide the election.

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