Evidence suggests that Washington had planned to move against Bin Laden in the summer. Was the attack on America a pre-emptive strike?
Did Bin Laden decide to get his retaliation in first? And did the new Bush administration make a horrible miscalculation by taking an ill-informed, "tough guy" approach to their fanatical Islamist opponent?
These are the troubling questions raised by the Guardian's disclosure at the weekend that the Taliban received a specific warning - passed during secret diplomacy in Berlin in July - that the Bush team had prepared a new plan to topple the entire Afghan regime militarily unless they handed Bin Laden over.
If it turns out that our future safety is in the hands of those who might possibly have averted the horror of September 11 by behaving more cautiously, then we owe it to history to establish the true record. But we can be certain that no one presently in charge in Washington will want to do that.
The Guardian's disclosures are proving controversial. Some analysts say Bin Laden had evidently prepared his suicide pilots up to a year beforehand, thus making Washington's behaviour in July beside the point. Others ask why US threats of military strikes in July should be of any more concern to Bin Laden than previous episodes, such as Clinton's rocketing of his camps.
We need to assess the evidence of the Bush team's foreign policy dealings this year to find the answers. This is made easier by the fact that two major players have now come out of the woodwork.
First, President Putin made clear he had tried to egg on the previous Clinton administration - without success - to act militarily against the whole Taliban regime: "Washington's reaction at the time really amazed me. They shrugged their shoulders and said matter-of-factly: 'We can't do anything because the Taliban does not want to turn him over'."
And then Clinton himself disclosed what limited - and equally unsuccessful - action he had been prepared to attempt by secret executive order. He said on Saturday: "I authorised the arrest and, if necessary, the killing of Osama bin Laden and we actually made contact with a group in Afghanistan to do it." Speaking to reporters in New York, he added: "We also trained commandos for a possible ground action, but we did not have the necessary intelligence to do it in the way we would have had to do it."
So Bush came into office this January against a background of American (and Clintonian) failure. While running for president the previous October, he said he was "saddened and angered" by the "cowardly attack" on the destroyer the USS Cole, and added: "There must be consequences."
As the outgoing senior official at the state department in charge of Afghanistan, Karl Inderfurth, remarked: "The Bush administration will have many urgent problems to face and, unfortunately, Afghanistan will be one of those because of terrorism and Bin Laden... Those problems are getting worse".
Although support from Pakistan, its southern neighbour, seemed to render the regime invulnerable, there were signs early this year that Washington was moving to threaten Afghanistan militarily from the north, via the wild former Soviet republics.
A US department of defence official, Dr Jeffrey Starr, visited Tajikistan in January. The Guardian's Felicity Lawrence established that US Rangers were also training special troops inside Kyrgyzstan. There were unconfirmed reports that Tajik and Uzbek special troops were training in Alaska and Montana.
And US General Tommy Franks visited Dushanbe on May 16, where he conveyed a message from the Bush administration that the US considered Tajikistan "a strategically significant country". On offer was non-lethal military aid. Tajikistan used the occasion to apply to join Nato's Partnership for Peace.
Shortly afterwards the Republican senator from Alabama who is vice-chairman of the Senate intelligence committee, Richard C Shelby, returned from a Gulf tour to bullishly tell the Washington Post that US counterterrorism officials were winning the war against Bin Laden. "He's on the run, and I think he will continue to be on the run, because we are not going to let up." He went on: "I don't think you could say he's got us hunkered down. I believe he's more hunkered down... He knows he's hunted."
Reliable western military sources say a US contingency plan existed on paper by the end of the summer to attack Afghanistan from the north. Throughout the spring, FBI information suggests terrorist suicide pilots were continuing to train at US aviation schools. But whatever contingency plan of theirs existed, no one pushed the terrorist button. By July 8, the Afghan opposition, Pakistani diplomats, and senior staff from the British Foreign Office, were gathering at Weston Park under UN auspices for private teach-ins on the Afghan situation.
And a couple of weeks later, another group gathered in a Berlin hotel. There, former state department official Lee Coldren passed on a message he had got from Bush officials: "I think there was some discussion of the fact that the United States was so disgusted with the Taliban that they might be considering some military action." Karl Inderfurth was there too, and former ambassador to Pakistan, Tom Simons.
The chilling quality of this private warning was that it came - according to one of those present, the Pakistani diplomat Niaz Naik - accompanied by specific details of how Bush would suceed where Clinton had failed.
The hawks in Washington could count on the connivance of Russian troops, and on facilities in such places as Uzbekistan and Tajikistan, already host to US military advisers.
The message that thus went back via Pakistan to the Taliban was that the hawks in Washington thought they were backing Bin Laden into a corner. Unfortunately, he decided to push his own button, instead.