As deliberations about the Obama administration's strategic direction in Afghanistan unfold, the White House is weighing whether al Qaeda, in fact, needs an Afghan safe haven -- an expanse of land under the protection of the Taliban -- to reconstitute its capability to attack the United States. Many noted scholars doubt it. In a recent Washington Post op-ed, Council on Foreign Relations President Richard Haass bluntly stated, "Al Qaeda does not require Afghan real estate to constitute a regional or global threat."

He's wrong. Although the group has been significantly weakened since late 2001, the only chance al Qaeda has of rebuilding its capability to conduct a large-scale terrorist operation against the United States is under the Taliban's umbrella of protection.

Objections like Haass's are rooted in the following arguments: that terrorists don't need physical space because they can plot online; that the London and Madrid bombings prove deadly attacks can be planned in restrictive, Western, urban locations under the noses of local security services; and that denying terrorists one safe haven will simply compel them to move to another lawless region.

I spent five years as a counterterrorism analyst for the Pentagon and rigorously studied plots from Madrid to London to 9/11. The above arguments may have merit in a piecemeal or abstract sense, but fall apart in the specific case of what we all dread: a large-scale, al Qaeda operation aimed at the United States.

It is certainly true, for example, that terrorist groups can accomplish much online. Individuals can maintain contact with groups via chat rooms, money can be transferred over the Web (if done with extreme caution), and plotters can download items like instruction manuals for bomb-making, photographs of potential targets, and even blueprints for particular buildings.

But all the e-mail accounts, chat rooms, and social media available will never account for the human touch. There is simply no substitute for the trust and confidence built by physically meeting, jointly conceiving, and then training together for a large-scale, complex operation on the other side of the world.

As the 9/11 plot developed, mastermind Khalid Sheik Mohammed (KSM) put the future operatives through a series of training courses along the Afghanistan-Pakistan border. Courses included physical fitness, firearms, close combat, Western culture, and English language. The 9/11 Commission report notes the extreme physical and mental demands KSM put on the participants -- even if the operation didn't require extensive firearms usage, KSM would have wanted the operatives to be proficient under intense pressure, should the need arise.

Juxtapose that with an online learning environment. While you can no doubt learn some amazing things from online courses, it is far preferable to have a dedicated professor physically present to supervise students and monitor their progress. Or think of it another way: You wouldn't want the U.S. Marine Corps to send recruits into battle without training under a drill instructor, would you? KSM was somewhere between a professor and sergeant.

Second, critics argue that the Madrid bombings of 2004 (which killed 191) as well those in London a year later (which killed 56) were largely -- though not entirely -- conceived, prepared, and executed within their respective countries, thus obviating the need for a safe haven.

True enough. However, unlike 9/11 (which killed nearly 3,000), those plots' successes were possible due to their simple concept and small scale. In both cities, the playbook was essentially the same: Four to eight individuals had to find a safe house, download bomb-making instructions, purchase explosive agents, assemble the devices, and deliver charges to the attack points. Without trivializing the tragic loss of life in the European attacks, building those explosive devices was akin to conducting a difficult high-school chemistry experiment.

On that scale, 9/11 was like constructing a nuclear warhead. In every sense, it was a grander vision, involving 20 highly skilled operatives infiltrating the U.S. homeland, who conducted a series of hijackings and targeted four national landmarks with enough know-how, preparation, and contingency plans to be success. In one instance, KSM taught the 9/11 operatives to shoot a rifle from the back of a moving motorcycle, just in case. You can't do that in someone's bedroom -- you need space, time, and the ability to work without worrying that the cops are listening in.

In other words, as a plot grows in number of operatives, scale of target, distance from base, and logistical complexity, so does the need for space to reduce the chances of being discovered and disrupted.

The final argument is that denying al Qaeda a safe haven is an exercise in futility: Drive Osama bin Laden from Afghanistan and he'd relocate to some place like Sudan, southern Algeria, Somalia, or other swaths of ungoverned territory. However, this logic makes two faulty assumptions: that al Qaeda is mobile, and that the group's international affiliates would automatically roll out the red carpet for the jihadi refugees.

Neither is true. Bin Laden and his senior and mid level cadre are well-known to intelligence services the world over. Any attempt to travel, let alone cross an international border (save Afghanistan-Pakistan) would fall somewhere between "utterly unthinkable" and "highly risky." Moving would further require massive reorientation of al Qaeda's financial operations and smuggling networks.

Nor would bin Laden's senior leaders be automatically welcomed abroad in areas their regional partners control. Though al Qaeda has established "franchise affiliates" in places like North Africa and Southeast Asia, relationships between al Qaeda's leadership and its regional nodes are extraordinarily complex. Groups like the North African affiliate "al Qaeda in the Islamic Maghreb" (AQIM) are happy to co-opt the al Qaeda "brand" for recruiting and financial reasons, but they don't necessarily share the al Qaeda senior leadership's ideological goals. AQIM is much more focused on attacking the Algerian government or foreign entities within the country, having not displayed much capability or desire for grandiose international operations. And last, recruits come to North Africa more often through independent networks in Europe, not camps along the Durand Line.  Think of the relationship like the one you have your in-laws: You might share a name, but you probably don't want them coming to visit for three full weeks.

Regional leaders aren't terribly loyal to senior leadership, either. Take Abu Musab al-Zarqawi, the deceased leader of the group's Iraq affiliate. He was summoned to bin Laden's side numerous times in an attempt to exert control as the Iraqi commander's tactics grew more grotesque and questionable. Zarqawi declined, not wanting to risk travel or accept instruction from bin Laden.

In the end, a safe haven along the Afghanistan-Pakistan border is as good as it gets for al Qaeda's chances to launch a large-scale attack against the United States. Certainly, smaller, less complex attacks could be planned without "Afghan real estate," but any such plot's death toll and long-term effect on American society will be far more limited.  Unfortunately, that's a risk President Barack Obama has to accept -- no amount of intelligence or counterterrorism operations can provide 100 percent security. But to avoid the Big One, the U.S. president's best bet is to deny al Qaeda the only physical space it can access.

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