IT was perhaps the most famous presidential briefing in history.

On Aug. 6, 2001, President George W. Bush received a classified review of the threats posed by Osama bin Laden and his terrorist network, Al Qaeda. That morning’s “presidential daily brief” — the top-secret document prepared by America’s intelligence agencies — featured the now-infamous heading: “Bin Laden Determined to Strike in U.S.” A few weeks later, on 9/11, Al Qaeda accomplished that goal.

On April 10, 2004, the Bush White House declassified that daily brief — and only that daily brief — in response to pressure from the 9/11 Commission, which was investigating the events leading to the attack. Administration officials dismissed the document’s significance, saying that, despite the jaw-dropping headline, it was only an assessment of Al Qaeda’s history, not a warning of the impending attack. While some critics considered that claim absurd, a close reading of the brief showed that the argument had some validity.

That is, unless it was read in conjunction with the daily briefs preceding Aug. 6, the ones the Bush administration would not release. While those documents are still not public, I have read excerpts from many of them, along with other recently declassified records, and come to an inescapable conclusion: the administration’s reaction to what Mr. Bush was told in the weeks before that infamous briefing reflected significantly more negligence than has been disclosed. In other words, the Aug. 6 document, for all of the controversy it provoked, is not nearly as shocking as the briefs that came before it.

The direct warnings to Mr. Bush about the possibility of a Qaeda attack began in the spring of 2001. By May 1, the Central Intelligence Agency told the White House of a report that “a group presently in the United States” was planning a terrorist operation. Weeks later, on June 22, the daily brief reported that Qaeda strikes could be “imminent,” although intelligence suggested the time frame was flexible.