Some Dates. Mostly from here.
June 22, 2001: CIA Director George Tenet is "nearly frantic" with concern about a terrorist attack.
June 28, 2001: Tenet writes a memo to national security adviser Condoleezza Rice: "It is highly likely that a significant al Qaeda attack is in the near future, within several weeks." Some officials say Tenet "repeated this so often that people got tired of hearing it."
July 5, 2001: Richard Clarke, the government's top counterterrorism official, tells officials of a dozen federal agencies, including the FAA, FBI, Secret Service and INS: "Something really spectacular is going to happen here, and it's going to happen soon." For six weeks, the US government is at its highest possible state of readiness against imminent terrorist attack.
August 6, 2001: As George Bush is briefed that al Qaeda might plan a hijacking within the US, the government had begun to lessen its alert of the previous month. Both Bush and Dick Cheney remain on vacation for the entire month.
September 4, 2001: The White House holds its first meeting on terrorism.
September 9, 2001: Defense Secretary Donald Rumsfeld threatens a presidential veto when the Senate proposed to divert $600 million from ballistic missile defense to counterterrorism.
September 10, 2001: Attorney General John Ashcroft rejects a proposed $58 million increase in FBI financing for counter-terrorism programs.