The chief lesson of 9/11 should have been that small bands of terrorists, using simple methods, can exploit loopholes in existing security systems. But instead, many preferred to engage in massive extrapolation: If 19 men could hijack four airplanes simultaneously, the thinking went, then surely al Qaeda would soon make an atomic bomb.

As a misguided Turkish proverb holds, "If your enemy be an ant, imagine him to be an elephant." The new information unearthed in Osama bin Laden's hideout in Abbottabad, Pakistan, suggests that the United States has been doing so for a full decade. Whatever al Qaeda's threatening rhetoric and occasional nuclear fantasies, its potential as a menace, particularly as an atomic one, has been much inflated.

The public has now endured a decade of dire warnings about the imminence of a terrorist atomic attack. In 2004, the former CIA spook Michael Scheuer proclaimed on television's 60 Minutes that it was "probably a near thing," and in 2007, the physicist Richard Garwin assessed the likelihood of a nuclear explosion in an American or a European city by terrorism or other means in the next ten years to be 87 percent. By 2008, Defense Secretary Robert Gates mused that what keeps every senior government leader awake at night is "the thought of a terrorist ending up with a weapon of mass destruction, especially nuclear." Few, it seems, found much solace in the fact that an al Qaeda computer seized in Afghanistan in 2001 indicated that the group's budget for research on weapons of mass destruction (almost all of it focused on primitive chemical weapons work) was some $2,000 to $4,000.

In the wake of the killing of Osama bin Laden, officials now have more al Qaeda computers, which reportedly contain a wealth of information about the workings of the organization in the intervening decade. A multi-agency task force has completed its assessment, and according to first reports, it has found that al Qaeda members have primarily been engaged in dodging drone strikes and complaining about how cash-strapped they are. Some reports suggest they've also been looking at quite a bit of pornography.

The full story is not out yet, but it seems breathtakingly unlikely that the miserable little group has had the time or inclination, let alone the money, to set up and staff a uranium-seizing operation, as well as a fancy, super-high-tech facility to fabricate a bomb. It is a process that requires trusting corrupted foreign collaborators and other criminals, obtaining and transporting highly guarded material, setting up a machine shop staffed with top scientists and technicians, and rolling the heavy, cumbersome, and untested finished product into position to be detonated by a skilled crew, all the while attracting no attention from outsiders.

The documents also reveal that after fleeing Afghanistan, bin Laden maintained what one member of the task force calls an "obsession" with attacking the United States again, even though 9/11 was in many ways a disaster for the group. It led to a worldwide loss of support, a major attack on it and on its Taliban hosts, and a decade of furious and dedicated harassment. And indeed, bin Laden did repeatedly and publicly threaten an attack on the United States. He assured Americans in 2002 that "the youth of Islam are preparing things that will fill your hearts with fear"; and in 2006, he declared that his group had been able "to breach your security measures" and that "operations are under preparation, and you will see them on your own ground once they are finished." Al Qaeda's animated spokesman, Adam Gadahn, proclaimed in 2004 that "the streets of America shall run red with blood" and that "the next wave of attacks may come at any moment."

The obsessive desire notwithstanding, such fulminations have clearly lacked substance. Although hundreds of millions of people enter the United States legally every year, and countless others illegally, no true al Qaeda cell has been found in the country since 9/11 and exceedingly few people have been uncovered who even have any sort of "link" to the organization.

The closest effort at an al Qaeda operation within the country was a decidedly nonnuclear one by an Afghan-American, Najibullah Zazi, in 2009. Outraged at the U.S.-led war on his home country, Zazi attempted to join the Taliban but was persuaded by al Qaeda operatives in Pakistan to set off some bombs in the United States instead. Under surveillance from the start, he was soon arrested, and, however "radicalized," he has been talking to investigators ever since, turning traitor to his former colleagues. Whatever training Zazi received was inadequate; he repeatedly and desperately sought further instruction from his overseas instructors by phone. At one point, he purchased bomb material with a stolen credit card, guaranteeing that the purchase would attract attention and that security video recordings would be scrutinized. Apparently, his handlers were so strapped that they could not even advance him a bit of cash to purchase some hydrogen peroxide for making a bomb. For al Qaeda, then, the operation was a failure in every way -- except for the ego boost it got by inspiring the usual dire litany about the group's supposedly existential challenge to the United States, to the civilized world, to the modern state system.

Indeed, no Muslim extremist has succeeded in detonating even a simple bomb in the United States in the last ten years, and except for the attacks on the London Underground in 2005, neither has any in the United Kingdom. It seems wildly unlikely that al Qaeda is remotely ready to go nuclear.

Outside of war zones, the amount of killing carried out by al Qaeda and al Qaeda linkees, maybes, and wannabes throughout the entire world since 9/11 stands at perhaps a few hundred per year. That's a few hundred too many, of course, but it scarcely presents an existential, or elephantine, threat. And the likelihood that an American will be killed by a terrorist of any ilk stands at one in 3.5 million per year, even with 9/11 included.

That probability will remain unchanged unless terrorists are able to increase their capabilities massively -- and obtaining nuclear weapons would allow them to do so. Although al Qaeda may have dreamed from time to time about getting such weapons, no other terrorist group has even gone so far as to indulge in such dreams, with the exception of the Japanese cult Aum Shinrikyo, which leased the mineral rights to an Australian sheep ranch that sat on uranium deposits, purchased some semi-relevant equipment, and tried to buy a finished bomb from the Russians.

That experience, however, cannot be very encouraging to the would-be atomic terrorist. Even though it was flush with funds and undistracted by drone attacks (or even by much surveillance), Aum Shinrikyo abandoned its atomic efforts in frustration very early on. It then moved to biological weapons, another complete failure that inspired its leader to suggest that fears expressed in the United States of a biological attack were actually a ruse to tempt terrorist groups to pursue the weapons. The group did finally manage to release some sarin gas in a Tokyo subway that killed 13 and led to the group's terminal shutdown, as well as to 16 years (and counting) of pronouncements that WMD terrorism is the wave of the future. No elephants there, either.