Michael Sheehan is on a one-man mission to put terrorist threats into perspective, which is a place they've rarely or ever been before. Already you can see it's going to be a hard slog. Fighting the inflated menace of Osama bin Laden has become big business, generating hundreds of billions of dollars for government agencies and contractors in what one friend of mine in the Washington policy-making stratosphere calls "the counterterrorist-industrial complex."

But Sheehan's got the kind of credentials that ought to make us stop and listen. He was a U.S. Army Green Beret fighting guerrillas in Central America in the 1980s, he served on the National Security Council staff under both President George H.W. Bush and President Bill Clinton, and he held the post of ambassador-at-large for counterterrorism from 1998 to 2000.

In those days Sheehan was among that persistent, relentless and finally shrill chorus of voices trying to warn the Clinton administration that Osama bin Laden and his boys represented a horrific danger to the United States and its interests. Days after the October 2000 suicide attack on the USS Cole in Yemen that killed 17 American sailors, experienced analysts like Sheehan at the State Department and Richard A. Clarke at the White House were certain Al Qaeda was behind it, but there was no support for retaliation among the Clintonistas or, even less, the Pentagon.

Clarke later wrote vividly about Sheehan's reaction after the military brass begged off. "Who the s--- do they think attacked the Cole, f---in' Martians?" Sheehan asked Clarke. "Does Al Qaeda have to attack the Pentagon to get their attention?"

We all know the answer to that question, of course. But what's interesting is not that Sheehan was so right, for all the good it did, or that President Bill Clinton and then President George W. Bush were so wrong not to pay attention. What's interesting is Sheehan's argument now that Al Qaeda just isn't the existential-twilight-struggle threat it's often cracked up to be. Hence the subtitle of his new book, "Crush the Cell: How to Defeat Terrorism Without Terrorizing Ourselves" (Crown, 2008).

The ideas Sheehan puts forth in a text as easy to read as a Power Point should be central to every security debate in the current presidential campaign. But given the personality politics that have dominated the race so far, that seems unlikely. Once again it's up to the public to figure these things out for itself.

"I want people to understand what the real threat is and what's a bunch of bull," Sheehan told me when I tracked him down a few days ago in one of those Middle Eastern hotel lobbies where you sip orange juice and lemonade at cocktail time. (He asked me not to say where, precisely, since the government he's now advising on policing and terrorism puts a high premium on discretion.)

Before September 11, said Sheehan, the United States was "asleep at the switch" while Al Qaeda was barreling down the track. "If you don't pay attention to these guys," said Sheehan, "they will kill you in big numbers." So bin Laden's minions hit U.S. embassies in Africa in 1998, they hit the Cole in 2000, and they hit New York and Washington in 2001—three major attacks on American targets in the space of 37 months. Since then, not one. And not for want of trying on their part.

What changed? The difference is purely and simply that intelligence agencies, law enforcement and the military have focused their attention on the threat, crushed the operational cells they could find—which were in fact the key ones plotting and executing major attacks—and put enormous pressure on all the rest.

"I reject the notion that Al Qaeda is waiting for 'the big one' or holding back an attack," Sheehan writes. "A terrorist cell capable of attacking doesn't sit and wait for some more opportune moment. It's not their style, nor is it in the best interest of their operational security. Delaying an attack gives law enforcement more time to detect a plot or penetrate the organization."

Terrorism is not about standing armies, mass movements, riots in the streets or even palace coups. It's about tiny groups that want to make a big bang. So you keep tracking cells and potential cells, and when you find them you destroy them. After Spanish police cornered leading members of the group that attacked trains in Madrid in 2004, they blew themselves up. The threat in Spain declined dramatically.

Indonesia is another case Sheehan and I talked about. Several high-profile associates of bin Laden were nailed there in the two years after 9/11, then sent off to secret CIA prisons for interrogation. The suspects are now at Guantánamo. But suicide bombings continued until police using forensic evidence—pieces of car bombs and pieces of the suicide bombers—tracked down Dr. Azahari bin Husin, "the Demolition Man," and the little group around him. In a November 2005 shootout the cops killed Dr. Azahari and crushed his cell. After that such attacks in Indonesia stopped.

The drive to obliterate the remaining hives of Al Qaeda training activity along the Afghanistan-Pakistan frontier and those that developed in some corners of Iraq after the U.S. invasion in 2003 needs to continue, says Sheehan. It's especially important to keep wanna-be jihadists in the West from joining with more experienced fighters who can give them hands-on weapons and explosives training. When left to their own devices, as it were, most homegrown terrorists can't cut it. For example, on July 7, 2005, four bombers blew themselves up on public transport in London, killing 56 people. Two of those bombers had trained in Pakistan. Another cell tried to do the same thing two weeks later, but its members had less foreign training, or none. All the bombs were duds.

Sheehan's perspective is clearly influenced by the three years he spent, from 2003 to 2006, as deputy commissioner for counterterrorism at the New York City Police Department. There, working with Commissioner Ray Kelly and David Cohen, the former CIA operations chief who heads the NYPD's intelligence division, Sheehan helped build what's regarded as one of the most effective terrorist-fighting organizations in the United States. Radicals and crazies of many different stripes have targeted the city repeatedly over the last century, from alleged Reds to Black Blocs, from Puerto Rican nationalists and a "mad bomber" to Al Qaeda's aspiring martyrs. But the police have limited resources, so they've learned the art of terrorist triage, focusing on what's real and wasting little time and money on what's merely imagined.

"Even in 2003, less than two years after 9/11, I told Kelly and Cohen that I thought Al Qaeda was simply not very good," Sheehan writes in his book. Bin Laden's acolytes "were a small and determined group of killers, but under the withering heat of the post-9/11 environment, they were simply not getting it done … I said what nobody else was saying: we underestimated Al Qaeda's capabilities before 9/11 and overestimated them after. This seemed to catch both Kelly and Cohen a bit by surprise, and I agreed not to discuss my feelings in public. The likelihood for misinterpretation was much too high."

It still is. At the Global Leadership Forum co-sponsored by NEWSWEEK at the Royal United Services Institute in London last week, the experts and dignitaries didn't want to risk dissing Al Qaeda, even when their learned presentations came to much the same conclusions as Sheehan.

The British Tories' shadow security minister, Pauline Neville-Jones, dismissed overblown American rhetoric: "We don't use the language of the Global War on Terror," said the baroness. "We actively eschew it." The American security expert Ashton Carter agreed. "It's not a war," said the former assistant secretary of defense, who is now an important Hillary Clinton supporter. "It's a matter of law enforcement and intelligence, of Homeland Security hardening the target." The military focus, he suggested, should be on special ops.

Sir David Omand, who used to head Britain's version of the National Security Agency and oversaw its entire intelligence establishment from the Cabinet Office earlier this decade, described terrorism as "one corner" of the global security threat posed by weapons proliferation and political instability. That in turn is only one of three major dangers facing the world over the next few years. The others are the deteriorating environment and a meltdown of the global economy. Putting terrorism in perspective, said Sir David, "leads naturally to a risk management approach, which is very different from what we've heard from Washington these last few years, which is to 'eliminate the threat'."

Yet when I asked the panelists at the forum if Al Qaeda has been overrated, suggesting as Sheehan does that most of its recruits are bunglers, all shook their heads. Nobody wants to say such a thing on the record, in case there's another attack tomorrow and their remarks get quoted back to them.

That's part of what makes Sheehan so refreshing. He knows there's a big risk that he'll be misinterpreted; he'll be called soft on terror by ass-covering bureaucrats, breathless reporters and fear-peddling politicians. And yet he charges ahead. He expects another attack sometime, somewhere. He hopes it won't be made to seem more apocalyptic than it is. "Don't overhype it, because that's what Al Qaeda wants you to do. Terrorism is about psychology." In the meantime, said Sheehan, finishing his fruit juice, "the relentless 24/7 job for people like me is to find and crush those guys."

As I headed into the parking lot, watching a storm blow in off the desert, it occurred to me that one day in the not too distant future the inability of these terrorist groups to act effectively will discredit them and the movement they claim to represent. If they did succeed with a new attack and the public and media brushed it off after a couple of news cycles, that would discredit them still more. The psychological victory would be ours for a change, and not only in our own societies but very likely in theirs. Or, to paraphrase an old Army dictum, if you crush the cells, the hearts and minds will follow.