While discussing the protocol of presidential safety in the case of an attack against the US in the program "Think" on PBS on Wednesday, the guest proclaimed we were hit by a "total surprise attack" on 9/11. In fact that claim is completely wrong, and many people knew that attack was coming.
As anyone can verify through declassified CIA documents displayed on the World-Wide Web (WWW), the CIA decoded Osama bin Laden's plans to attack the Twin Towers of the World Trade Center (WTC) about 3 years before 9/11. They soon labelled these plans as the "bin Laden problem" and explored options for countering them. Most of these declassified documents were included in the 9/11 Commission Report released in 2003. They examined bin-Ladin's attacks on the USS Cole, his interest in biological and radiological weapons, and how Afghanistan was an incubator for terrorism.
National Security Advisor Richard Clarke went to some length to advise members of incoming George W Bush Admistration in January of 2001 of the terrorism threat from Osama bin Laden's al Quaeda group near Afghanistan (see Clarke's book Again All Enemies). The Congressional report said in May, 2001 that intelligence officials received information that indicated "a group of bin Laden supporters was planning attacks in the United States with explosives." The CIA reported to the President on May 1 that "a group presently in the US was planning a terrorist operation". George Tenet, the director of the CIA communicated personally with National Security Advisor Clarke, and they were soon both convinced that a major series of attacks was about to come. The FBI as well as FAA and other senior security officials joined Clarke.
The CIA reported that Khalid Sheik Mohammed was recruiting people to travel to the US, likely to conduct terrorist attacks on bin Laden's behalf. On June 22, 2001, the daily brief to President Bush stated that the al Quaeda strikes could be "imminent". The CIA prepared an analysis that all but pleaded with the White House to accept that the danger from bin Laden was real. By the White House meeting on July 5 the CIA had briefed security officials of several different agencies on the al Quaeda threat of terrorists striking within the US, warning that a strike was imminent. As CIA Director George Tenet described "The system was blinking red" (see The 9/11 Comission Report).
President Bush was told personally in a secret briefing on August 6, 2001, more than a month before 9/11, that supporters of Osama bin Laden planned an attack within the United States with explosives and wanted to hijack airplane. He received the full report "Bin Laden determined to strike within the US".
On September 4, 2001 Clarke called an urgent meeting for what he believed was an imminent attack. Both he and George Tenet spoke passionately about the urgency of the al Quaeda threat, and the possibility of killing 100s of Americans. Secretary of Defense Rumsfeld, like Assistant Secretary Wolfowitz, downplayed the significance by bringing up other terrorists, particularly Iraqi terrorists. Condeleeza Rice asked Clarke to finalize a policy document & send it to President Bush for a signature.
On that day of the September 4 meeting Richard Clarke sent Condeleeza Rice an impassioned note criticizing the US counterterrorism efforts. He wrote that the real question was before the meeting principals was "are we serious about dealing with the Al Quaeda threat?...Decision makers should imagine themselves on a future day when the group had not succeeded in stopping the Al Queda attacks & 100s of Americans lay dead... What would those decision makers wish they had done earlier? That future day could happen at any time." One week later it did.
So, many government employees knew of the coming 9/11 attack. That was so true that there were massive investments in put options for stocks that were anticipated to do badly in the attack. But most American ctizens were surprised by 9/11, because elected government officials did not warn them.