Americans must not allow Bin Laden to influence their vote or subvert their democracy

The image of a priestly Osama bin Laden calmly advising Americans that their security rests neither with George Bush nor with John Kerry but in their own hands has brought the US election campaign full circle in menacing style. This reminder of the 11 September atrocities is where President Bush cynically began his campaign on Labour Day and where he would surely have hoped to conclude it had Mr Kerry not forced a multitude of other pressing issues, from the Iraq war to the economy, on to the agenda.

Now, the weekend before the vote, with the opinion polls effectively tied, Bin Laden, 11 September and the "war on terror" have all landed back in the centre of this campaign. For those American voters who listen to what Bin Laden has to say - the words contained in the edited sections of the tape that the Arab television station, al-Jazeera, decided to broadcast and which were then reported back to the US - the impact could hardly be other than neutral.

There are words of criticism, warning and comfort for both candidates; sentiments that each could interpret as favourable to him. The very existence of the tape also cuts both ways. Mr Bush can argue that it shows the continuing validity of his "war on terror". Mr Kerry can counter that it proves the failure of the Bush administration's efforts to take Bin Laden "dead or alive". The two rational responses to Bin Laden's sermonising are indifference or fury: indifference in that his words do nothing to change the balance of advantage; fury that any outsider should have presumed to sway a democratic election, and particular fury that the mastermind of 11 September should have dared to exploit an American election for his own intimidatory, self-aggrandising ends.

First indications from opinion polls and from the straw polls of our own correspondents on the ground are that this is indeed how US voters are responding. For as much as 15 per cent of the electorate, Bin Laden's intervention anyway comes too late. Opportunities for early voting have allowed several million Americans to cast their votes in the two weeks before election day. And whether early voting is viewed as an enlightened convenience or a distortion of the electoral process, it necessarily dulls the impact of last-minute surprises - which in this case is no bad thing.

So far, then, so good. There must remain, however, at least a sliver of doubt. For as long as Mr Kerry allowed him to get away with it, Mr Bush played unscrupulously - and effectively - on Americans' fear of a new 11 September. Just two weeks before polling day, his campaign pandered yet again to that fear in a campaign advertisement that depicted prowling wolves threatening America. And the question remains: when they go into the polling booth tomorrow, what images will Americans see? Will it be the image of Osama bin Laden gloating over the fallen trade towers, with the wolves prowling around, or will it be the images of mayhem in Iraq, shackled Enron executives indicted for fraud, parents without medical insurance for themselves or their children; pensioners travelling to Canada to buy medicine they can afford? Will their vote be dictated by fear or inspired by the hope and possibility of change?

The reappearance of Osama bin Laden in the very last days of this campaign crystallises that choice - the very same choice that American voters confronted so many months ago when the candidates contested the first primaries in Iowa and New Hampshire. Now, once again, George Bush's promise to keep Americans safe is pitted against John Kerry's appeal to weigh George Bush's disastrous record in office. Now, once again, there is a risk that the fear factor, conjured up anew by Bin Laden, will stifle all other considerations. Mr Kerry must appeal to the voters' good sense and do his utmost to ensure that Mr Bush and Bin Laden together do not drown out his arguments. With the former president, Bill Clinton, we hope against hope that America will choose optimism over fear.