US asks a disturbing question: What did the President know?

At last the dam has broken. For eight months America has tiptoed around the most disturbing questions of all surrounding 11 September. Did the Bush administration fail to act on the evidence it had in hand, and prevent the worst terrorist attack in modern history?

From time to time the issue would crop up, only for it to be deflected by the feeling that the moment was still too close, and the argument that a post mortem which was bound to be painful for the country's security and intelligence services might interfere with the war against terrorism those agencies were helping to wage.

But all these considerations have been swept away by the disclosure that President George Bush was warned by the CIA in the first week of August that al-Qa'ida might be planning to hijack aircraft.

That in itself does not greatly advance the sum total of public knowledge on what was known before the attacks. Five days afterwards, the Vice-president Dick Cheney acknowledged that US intelligence agencies had indications that something was in the offing, and if the White House is to be believed, the intelligence briefing Mr Bush received while vacationing at his ranch in Texas was no more specific.

But the very fact that something was on paper before the eyes of the President has changed the dynamic, at a watershed political moment. The shooting war against al-Qa'ida is winding down, and the trail of Osama bin Laden has gone cold. Meanwhile the mid-term elections in November, in which control of both Houses is at stake, grow steadily nearer.

Thus far the Democrats have held back from a frontal attack on a President whose approval ratings remain around 70 per cent – in normal times an extraordinary level of popularity for any occupant of the White House. To challenge Mr Bush's handling of the war was unpatriotic. But now they sense a chink in the President's handling of 11 September which can be decently exploited.

No one – with the exception of the New York Democratic Congressman Jerrold Nadler – has gone so far as to suggest that Mr Bush, by his negligence, was in any way to blame for what happened. But the White House is being criticised on two counts.

The first is the relatively trivial one of failing to notify the specialist Senate and House committees back in August of what the White House had learnt. For Capitol Hill, ever sensitive of its prerogatives, that is a sin of some magnitude. In the country at large, it is unlikely to resonate greatly.

Far more serious is the accumulating evidence that the CIA and the FBI failed to "connect the dots" – that the two agencies did not draw the right conclusions from the pieces of separate evidence in hand by late summer. They include:

Warnings from some European intelligence services earlier in the year that something was afoot.

The Attorney General John Ashcroft stopped using ordinary commercial jets in early summer after an internal security warning.

A request from an FBI agent in Phoenix, Arizona, for an investigation of Middle Eastern men training at flight schools in America. The memorandum mentioned Mr bin Laden by name, and said the training might be for terrorist purposes.

Data reaching the CIA that something was intended for the Independence Day holiday of 4 July.

The arrest of Zacharias Moussaoui, the suspected "20th hijacker", who had raised suspicions during flight training in Minnesota by expressing little interest in take-off and landing.

Individually, and even together, these pieces of evidence did not provide conclusive evidence that an attack was imminent. For that reason the heightened alerts that were ordered were not made public.

What they have highlighted however is the inadequate collaboration between the CIA, responsible for overseas intelligence, and the FBI, in charge of domestic security. This is an old problem – and one reason why superspies Aldrich Ames of the CIA and the FBI agent Robert Hanssen went so long undetected. If there are to be scapegoats, they are likely to come from the agencies themselves. The position of George Tenet, the CIA director, seems especially vulnerable. Within days of the attacks, Richard Shelby, the senior Republican on the Senate Intelligence Committee, was demanding his resignation.