Kerry prepares for 15 minutes that could decide the election

George Bush and John Kerry are in purdah this weekend, intensely prepping for next Thursday's first presidential debate - a showdown on terrorism, Iraq and national security at the University of Miami which might settle the outcome of the 2 November election.

To be sure, the word "debate" is something of a misnomer. The rules have been worked out with the stifling precision of a superpower arms pact. The two candidates will not be able to question each other directly, and will not be allowed within a certain distance of each other. Anyone looking for spontaneity, and real intellectual cut and thrust, is likely to be disappointed.

The 32-page "memorandum of understanding" dictates everything, from the height of the lecterns (50 inches) to the distance between them (10 feet), to the temperature in the hall. It specifies the exact type of stool (with footrest and back support) to be used for the second debate. This will be a "town hall" session with swing voters whose questions will be cleared by the moderator beforehand. Woe betide anyone who dares change their question on the air. They will be immediately cut off.

Each side has made concessions. The Bush campaign, which wanted only two 90-minute debates, finally accepted the three originally proposed by the Commission for Presidential Debates. The Kerry team, however, agreed to move up national security, Mr Bush's strongest issue, to the first debate, always the most watched and most influential.

On Thursday, the domestic TV audience may reach 80 million, not to mention the uncounted millions of viewers around the world. "The first 15 or 20 minutes will be crucial," says Scott Reed, who managed Bob Dole's losing Republican campaign of 1996.

Already the bizarre ritual of lowering expectations is in full swing. Listen to each side, and their man is sure to lose. Democrats who normally deride Bush as an inarticulate buffoon now hail him as the finest public speaker since Demosthenes. The Bush campaign plays the same game, building up John Kerry as a surefire winner - "the greatest debater since Cicero" in the words of a straight-faced Matthew Dowd, a chief Bush/ Cheney strategist.

Both sides, however, have good reason for caution. Mr Kerry is indeed a pretty competent debater, fast on his feet and a formidable marshaller of an argument. Democrats are only too well aware that Mr Bush is all too easily underestimated - just ask Al Gore. No one ever disputed Mr Bush's folksy charm. But articulateness is another matter. A single unmangled sentence thus counts as a mighty victory.

The tactics also reflect the hugeness of the stakes on Thursday. Debates have changed elections - in 1976 a Gerald Ford gaffe about Eastern Europe wrecked his foreign policy credibility, while four years later Ronald Reagan convinced wavering voters he was not an extremist fool who could not be trusted with the presidency.

This week, a solid performance by Mr Bush would probably finish off his Democratic challenger, already lagging in the polls and far behind the President in voters' assessment of who is best able to "keep the country safe" - the central subject of the evening.

But the debates have at last put Mr Kerry on the same stage, as the President's equal. A strong showing in a direct match-up might just change the momentum of what is still a fairly close-fought race.

In the past week he has completely changed tactics, taking the offensive and lambasting the President for a misguided focus on Iraq, at the expense of the real threat posed by al-Qa'ida. The bungled aftermath of the invasion, Mr Kerry argues, has made America less, rather than more safe.

The key question, though, is whether the Democrat can break the link Mr Bush has established in voters' minds between Iraq and the "war on terror". Iraq is presented as "the central front in that war", an approach that allows the President to dodge the awkward question of whether the 2003 invasion has made America even more of a terrorist target than it was before.

Democrats believe that Mr Kerry's sharper rhetoric is starting to sow doubts in voters' minds about Mr Bush's competence; might not that vaunted single-mindedness merely be a pig-headed refusal to face facts? The first debate, however stilted its format, could provide an answer - and in the process settle the election.