Should the United States leave any troops in Afghanistan after 2014? Would that prevent the return of militant jihadis who could threaten nuclear-armed Pakistan next door?

With most or all U.S. forces set to leave Afghanistan by 2014, President Obama is considering a "zero option," which would mean relying on drone strikes and special forces to counter militants, while leaving overall security to shaky Afghan forces.

Is this the best approach, I asked Gen. Stanley A. McChrystal, who, as U.S. commander in Afghanistan, presided over the U.S. troop "surge," but also led the Joint Special Operations Command in its fight against al-Qaeda in Iraq (AQI). His account of his Iraq and Afghan roles, My Share of the Task: A Memoir, has just been published. (He will speak at noon at Philadelphia's Free Library.)

"It's dangerous to view drone strikes as a strategy in itself," the general said firmly in a phone interview. "I fear it is a tempting approach that may be overweighted."

So what does he think the United States should do?

First some background. McChrystal's memoir gives a gripping account of the complex counterterrorism mission that killed AQI leader Abu Musab al-Zarqawi. Yet, when he took command in Afghanistan, the general concluded that a counterterrorism strategy alone would not prevent the country's collapse; nor would it prevent militants from taking control of territory and terrorizing the people.

So McChrystal adopted a classic "counterinsurgency" approach (known as COIN), the concept promoted by Gen. David Petraeus in Iraq. McChrystal requested a surge of U.S. troops "as a bridge" to protect Afghans in key areas, in hopes of buying time for the training of Afghan forces and the strengthening of the Afghan government. "I thought it would work," the general said. "The real question was Afghans' confidence. It was all about their perceptions of impending abandonment."

In other words, if rural Afghans thought U.S. forces would have their back, they would have the courage to stand up to the Taliban - even as their own government developed the strength to protect them. McChrystal also believed it was critical to treat Afghans with respect, and to limit civilian casualties.

The book details the tensions that arose between McChrystal and the White House over how many "surge" troops should be dispatched (he wanted 40,000 and got 30,000), and over Obama's announcement that he would begin withdrawing surge forces in July 2011.

"I cited concerns that [the announcement] would give the Taliban a sense that if they survived until that date, they could prevail," the general writes. But he concluded that a surge of 30,000 was "something we could work with."

Fast-forward. After the recent departure of the last surge troops, we can see that they stabilized certain areas of Afghanistan, but national and local Afghan government never kept their part of the bargain. Burdened by corruption, bereft of government services, Afghans once again fear pending abandonment by international forces. They have no certainty that their own security forces can protect them. And the Taliban is once again making serious inroads.

Meantime, McChrystal was fired by Obama in 2010 over a Rolling Stone article that quoted him and his staff as making critical remarks about White House officials.

COIN theory is now in disfavor. In an age of austerity, Obama has adopted a far more limited counterterrorism strategy, while promising to maintain a "strategic partnership" with Kabul.

Yet McChrystal still believes more is needed. "I still think the issue of [Afghan] confidence is crucial," he told me. "When President Obama talks about partnership . . . the Afghan people have to believe there is some sinew to that - that we are a reliable ally."

If Afghans think Washington is committed to the partnership, McChrystal believes their army, now better trained, can hold together - with U.S. assistance in training, air support and logistics, and intelligence. Educated Afghans would be less likely to flee. The Taliban might be persuaded to make a political deal - with Pakistan more willing to facilitate such a deal.

On the other hand, if Obama goes for a "zero option" or a tiny, symbolic number of troops (rather than the 9,000-15,000 the military reportedly seeks), "it would be very difficult to convince Afghans there was a strategic partnership." U.S. diplomats would be hunkered down in Kabul. Afghan and Pakistani officials might become even more hostile to drone strikes.

"I became convinced [in Afghanistan] that counterterrorism is only effective if meshed with a wider strategy," McChrystal said. As for the use of drones, "It is a very limited approach that gives the illusion you are making progress because you are doing something."

When deciding if any troops should stay on in Afghanistan in 2014, White House officials would be wise to consider these concerns.

E-mail Trudy Rubin at