There is considerable debate in Washington over whether the United States could plausibly have “connected the dots” leading to September 11. Useful insights have emerged from this debate. One insight is the danger of continuing to separate foreign and domestic intelligence related to terrorism, the institutional reflection of which is the separation of the national security and law enforcement functions. Steps are underway to bridge this historical chasm. Another insight, stressed by the attorney general and FBI director, is the need to encourage and reward FBI agents to prevent terror crimes from happening in the first place rather than “solving” them after they have occurred.

Most Americans were probably not shocked to learn on September 12 that the U.S. government did not have advance information about the dozen or so individuals residing in the country who plotted and took part in the airline suicide bombings of September 11. They probably were deeply disturbed to learn, however, that the government was as heedless of the tactic used as it was of the perpetrators. The airline security system inspected for guns and bombs, not knives; aircrews were trained to deal with hijackers who sought hostages or conveyance to Cuba, not kamikaze attack. In retrospect, a huge gap existed in the U.S. air safety system. Terrorists detected it before the security system did—and exploited it.

To avoid tactical surprise of this kind, the homeland security effort needs to adopt a standard mechanism of military organizations: competing red and blue teams. The red team projects itself imaginatively into the terrorist’s shoes and tries to devise attack tactics. The blue team tries to design countermeasures. When the United States developed the first stealth aircraft, for example, the air force created a red team to try to detect and shoot it down. When the red team identified a weakness in the stealth design, the blue team was charged to fix it, systematically balancing risk of detection against the cost and inconvenience of countermeasures

The result is a world today seemingly without a major threat to the United States, and the U.S. is now enjoying a period of peace and influence as never before. But while this situation is to be savored by the public, foreign policy and defense leaders should not be complacent. This period of an absence of threat challenges these leaders to find the vision and foresight to act strategically, even when events and imminent threats do not compel them to do so.

To understand the dangers and opportunities that will define our nation’s strategy in the new era, we must see the post-Cold War world the way George Marshall looked upon Europe after World War II, and return to prevention. In essence, we now have another chance to realize Marshall’s vision: a world not of threats to be deterred, but a world united in peace, freedom, and prosperity. To realize this vision, we should return to Marshall’s strategy of preventive defense.

Preventive Defense is a concept of defense strategy for the United States in the post-Cold War Era. It stresses the need to anticipate security dangers which, if mismanaged, have the potential to re-create Cold War-scale threats to U.S. interests and survival. The foci of Preventive Defense are: proliferation of weapons of mass destruction, catastrophic terrorism, "loose nukes" and other military technology from the former Soviet Union, Russia’s post-Cold War security identity, and the peaceful rise of China.

Readers should imagine the possibilities for themselves, because the most serious constraint on current policy is lack of imagination. An act of catastrophic terrorism that killed thousands or tens of thousands of people and/or disrupted the necessities of life for hundreds of thousands, or even millions, would be a watershed event in America’s history. It could involve loss of life and property unprecedented for peacetime and undermine Americans’ fundamental sense of security within their own borders in a manner akin to the 1949 Soviet atomic bomb test, or perhaps even worse. Constitutional liberties would be challenged as the United States sought to protect itself from further attacks by pressing against allowable limits in surveillance of citizens, detention of suspects, and the use of deadly force. More violence would follow, either as other terrorists seek to imitate this great "success" or as the United States strikes out at those considered responsible. Like Pearl Harbor, such an event would divide our past and future into a "before" and "after." The effort and resources we devote to averting or containing this threat now, in the "before" period, will seem woeful, even pathetic, when compared to what will happen "after." Our leaders will be judged negligent for not addressing catastrophic terrorism more urgently.

Using imagination, we hope now to find some of the political will that we know would be there later, "after," because this nation prefers prevention to funereal reconstruction. When this threat becomes clear the President must be in a position to activate extraordinary capabilities. The danger of the use of a weapon of mass destruction against the United States or one of its allies is greater at this moment than it was during the Cold War, or at least since 1962. The threat of catastrophic terrorism is therefore a priority national security problem, as well as a major law enforcement concern. The threat thus deserves the kind of attention we now devote to threats of military nuclear attack or of regional aggression, as in the Defense Department’s major regional contingencies that drive our force planning and the resources we devote to defense.

The first enemy of imagination is resignation. Some who contemplate this threat find the prospects so dreadful and various that they despair of doing anything useful and switch off their troubling imagination. They are fatalistic, like someone contemplating the possibility of a solar supernova, and turn their eyes away from the threat. Some thinkers reacted the same way at the dawn of the nuclear age, expecting doom to strike at any hour and disavowing any further interest in the details of deterrence as a hopeless venture. But as in the case of nuclear deterrence, the good news is that more can be done.