If John Kerry becomes president of the US, Islamic fanatics the world over will celebrate

It might seem to the Iranians that they were dealing with a weak and indecisive president whom they could overawe

If Clio, the muse of history, did exist, we would already know the result of the American election. On past form, the lady is a minx with a taste for mischief. In that case, President Bush would win by carrying the Electoral College, even though he again came second in the popular vote. Moreover, in two key states, the Republican margin of victory would be fewer than 100 votes. So on Wednesday 3 November, 100,000 Democrat lawyers would file suit.

I have recently talked to a number of American pollsters. None of them would rule out such an outcome. Whatever their partisanship, they all devoutly hope that it will not happen; it would be bad for public confidence in the American political system. I have a feeling that the result will be Bush 51 per cent, Kerry 47, Nader 2, which would give the President a comfortable margin in the Electoral College. But I would not wish to reinforce my hunch with a large wager. The outcome could hang on a chad.

The uncertainty is causing strain in Europe as well as in the US. Never has a US election aroused such passionate feelings abroad, almost all of them hostile to Mr Bush. A sizeable majority of Europeans believe that whatever Mr Kerry's qualities, or lack of them, nothing could be worse than the incumbent president. Yet that is a highly debatable claim even on liberal assumptions. There are good reasons to argue that a Kerry presidency would do nothing to improve US-European relations and that it would make the world much more dangerous.

Senator Kerry has spent most of the campaign inviting his fellow Americans to picture him as they would wish him to be: one reason why he deserves to lose. We do not know what he really thinks about anything. We certainly have no idea what he would do about Iraq. He might well be tempted to prove his machismo by stepping up the military effort, at least in the short term. This would be even more likely if Richard Holbrooke were to become secretary of state.

Though Mr Holbrooke can be accused of many things, the charge sheet would not include wimpishness. By temperament, he is no diplomat: his negotiating manner is Donald Rumsfeld's rather than Colin Powell's. He is reminiscent of the tough-minded characters who advised Presidents Kennedy and Johnson on Vietnam. He resembles the young Robert McNamara, not the older, penitent one. It is likely that Mr Holbrooke would urge increased military activity in Iraq backed up by vigorous diplomacy. If so, he would almost certainly get his way.

He would also try to involve the UN and the Europeans. This would be widely welcomed, until the reasons for the involvement were made manifest. Mr Holbrooke is the last man who would surrender US primacy in any major mission. The allies might be allowed a say, but only if they paid for their place at the table with a significant troop deployment. Were they to refuse to do so, they would quickly encounter the abrasive aspects of Mr Holbrooke's personality, which are well remembered by the Europeans who dealt with him over Bosnia and Kosovo.

If Senator Kerry were to win, it could be that by next Easter the Europeans would be discovering that even under a president who spoke French and ate cheese, key elements in the administration were regarding them as surrender monkeys. It would be amusing to listen out for the first European liberal to protest that he was as bad as George Bush.

But Europe is not the most important reason for scepticism about a Kerry presidency, or for anxiety about a Bush defeat. If President Bush lost, the discreet rejoicing in the chancelleries of Europe would be as nothing to the political ecstasy throughout much of the Islamic world. That could be a mortal threat to the West.

The Islamic fanatics would conclude that they had been proved right. Hit the West and it will probably retaliate, inflicting short-term defeats. But these will only be short term. The West has neither the self-confidence nor the will to slog on in the face of adversity and casualties.

These Islamic fanatics have no interest in minimising their own casualties. They will believe that the US electorate has voted out a President because the martyrs in Iraq had managed to kill a mere thousand Americans. They will also be aware of the result in Spain, whereas Australia has hardly registered on their radar screen. They will be emboldened in the assumption that despite the West's potential military might, we are an alliance of haemophiliacs. All this could make a terrorist attack in Britain much more likely before our next election.

It would also complicate matters in Iran. If they do not already have nuclear weapons, the Iranians are on the verge of possessing them, as well as rockets which could reach Israel. Whatever the West's response to this, it is unlikely that the Israelis would stand idly by.

The EU has put a lot of effort into its Iran diplomacy, without much success.Iran has a complex regime structure. Some highly placed fanatics would be indifferent to the consequences of a nuclear exchange with Israel, because they would be content for Iran to suffer terrible damage if the Israeli enemy were destroyed. There are others who would not wish to see their country destroyed despite the intensity of their Islamic convictions. They would also be aware of the consequences of a nuclear strike against Israel if George Bush were still president. In those circumstances, America would defend its ally and little of Iran would survive.

This is the most dangerous problem facing the world at the moment, one reason why not many people wish to discuss it. There is one obvious conclusion to be drawn. If President Bush is re-elected, the Iranians will know where they stand. Should they become able to deploy weapons of mass destruction, and the Israelis strike at them, the US would be on Israel's side. Should Iran seek to retaliate against Israel with WMD, it would find itself at war with America, willing to use WMD. Iran could face obliteration.

That is hardly likely to reassure anyone in Europe who is already worried about Mr Bush's belligerent tendencies. Yet it might not be a bad thing for world peace. If the Iranians knew that there was no way to strike at Israel without risking everything, they might be less inclined to strike at Israel. They might even be more inclined to listen to European diplomats.

It is possible that Iran would be no less at risk under President Kerry. It is probable that he would be at least as sensitive to Israel's vital interests as President Bush. But there would be a dangerous and destabilising element of uncertainty. It might seem to the Iranians that they were dealing with a weak and indecisive president whom they could overawe by the threat of terror.

No one would ever make that assessment of George Bush. Europeans believe that he is a dangerous man. They are wrong. The truth is that we live in a dangerous world. He is the best candidate to guide us through the dangers.