It has now been nine years since al Qaeda attacked the United States. It has been nine years in which the primary focus of the United States has been on the Islamic world. In addition to a massive investment in homeland security, the United States has engaged in two multi-year, multi-divisional wars in Iraq and Afghanistan, inserted forces in other countries in smaller operations and conducted a global covert campaign against al Qaeda and other radical jihadist groups.

In order to understand the last nine years you must understand the first 24 hours of the war — and recall your own feelings in those 24 hours. First, the attack was a shock, its audaciousness frightening. Second, we did not know what was coming next. The attack had destroyed the right to complacent assumptions. Were there other cells standing by in the United States? Did they have capabilities even more substantial than what they showed on Sept. 11? Could they be detected and stopped? Any American not frightened on Sept. 12 was not in touch with reality. Many who are now claiming that the United States overreacted are forgetting their own sense of panic. We are all calm and collected nine years after.

At the root of all of this was a profound lack of understanding of al Qaeda, particularly its capabilities and intentions. Since we did not know what was possible, our only prudent course was to prepare for the worst. That is what the Bush administration did. Nothing symbolized this more than the fear that al Qaeda had acquired nuclear weapons and that they would use them against the United States. The evidence was minimal, but the consequences would be overwhelming. Bush crafted a strategy based on the worst-case scenario. Bush was the victim of a decade of failure in the intelligence community to understand what al Qaeda was and wasn't. I am not merely talking about the failure to predict the 9/11 attack. Regardless of assertions afterwards, the intelligence community provided only vague warnings that lacked the kind of specificity that makes for actionable intelligence. To a certain degree, this is understandable. Al Qaeda learned from Soviet, Saudi, Pakistani and American intelligence during the Soviet occupation of Afghanistan and knew how to launch attacks without tipping off the target.

The greatest failure of American intelligence was not the lack of a clear warning about 9/11 but the lack, on Sept. 12, of a clear picture of al Qaeda's global structure, capabilities, weaknesses and intentions. Without such information, implementing U.S. policy was like piloting an airplane with faulty instruments in a snowstorm at night. The president had to do three things: First, he had to assure the public that he knew what he was doing. Second, he had to do something that appeared decisive. Third, he had to gear up an intelligence and security apparatus to tell him what the threats actually were and what he ought to do. American policy became ready, fire, aim.

In looking back at the past nine years, two conclusions can be drawn: There were no more large-scale attacks on the United States by militant Islamists, and the United States was left with the legacy of responses that took place in the first two years after 9/11. This legacy is no longer useful, if it ever was, to the primary mission of defeating al Qaeda, and it represents an effort that is retrospectively out of proportion to the threat. If I had been told on Sept.12, 2001, that the attack the day before would be the last major attack for at least nine years, I would not have believed it. In looking at the complexity of the security and execution of the 9/11 attack, I would have assumed that an organization capable of acting once in such a way could act again even more effectively. My assumption was wrong.

Al Qaeda did not have the resources to mount other operations, and the U.S. response, in many ways clumsy and misguided and in other ways clever and targeted, disrupted any preparations in which al Qaeda might have been engaged to conduct follow-on attacks. Knowing that about al Qaeda in 2001 was impossible. Knowing which operations were helpful in the effort to block them was impossible, in the context of what Americans knew in the first years after the war began. Therefore, Washington wound up in the contradictory situation in which American military and covert operations surged while new attacks failed to materialize. This created a massive political problem. Rather than appearing to be the cause for the lack of attacks, U.S. military operations were perceived by many as being unnecessary or actually increasing the threat of attack.