Many Americans probably wonder why President Obama didn’t call for a bigger troop pullout from Afghanistan.

Having recently returned from Afghanistan and Pakistan, I think he could have made a stronger case for his decision to bring home only 10,000 troops by the end of this year. (The rest of the 33,000 “surge” troops he has deployed will return no later than September 2012, with a full transition to Afghan security control supposedly occurring by 2014.)

The public needs more details to grasp why a slow exit is preferable to just bringing the troops home.

Anyone can understand why the American public is getting restless ― 10 years after we invaded Afghanistan. Our economy sags as we continue to spend $10 billion a month for the military operation. Public confusion is compounded by the fact that Osama bin Laden was hiding in a Pakistani military town, not on some Afghan mountain. Meantime, senior administration officials say there’s no sign that transnational terrorists are using Afghanistan as a launch pad.

So why are we still in Afghanistan at all?

The president explains that our goal is to stabilize the country sufficiently to prevent al-Qaida and its allies from re-establishing bases there. Yet many Americans question the seriousness of this threat, or why we can’t prevent it with drones or Special Forces, rather than regular soldiers.

Here’s what I think Obama could have added to his explanation to make a stronger case.

First, the threat: Yes, it’s true that the post-bin Laden core of al-Qaida is hiding in Pakistan (while affiliated groups operate in Yemen and elsewhere). But al-Qaida’s militant allies, including some Afghan Taliban groups, highly dangerous Pakistani Taliban, and some foreign elements, have set up safe havens in the eastern provinces of Afghanistan that border Pakistan.

Some of these groups want to attack Western targets. Moreover, Pakistani Taliban are using eastern Afghanistan as a safe haven from which to hit at the Pakistani military across the border. Their goal is to undermine the nuclear-armed Pakistani state and get their hands on nuclear materiel.

U.S. officials won’t publicly discuss their deep worry about Pakistan’s vulnerability to Islamists. Unlike Iraq, which did not have al-Qaida or nukes, Pakistan contains jihadis with global goals and nuclear weapons.

Yes, those weapons are under several layers of Pakistani military control. But the country is in deep economic trouble and has a totally dysfunctional civilian government; this disarray provides fertile ground for militant preaching.

Meantime, Pakistan’s army is bogged down in its fight against its own Taliban. And the army’s ranks have been penetrated by Islamists who’ve been able to attack key military installations.

Too rapid a U.S. drawdown in Afghanistan could further destabilize Pakistan. It would also undermine U.S. military plans to focus more on clearing jihadis from eastern Afghanistan after solidifying military gains in the south.

Second, the exit strategy: The administration recognizes that Afghan stability can’t be achieved by military force. But no one has figured out how to reach a political solution that will end the fighting.

The administration, along with the Afghan government, has put out feelers to the Afghan Taliban to see if some groups would contemplate a deal short of returning to full power. This is a delicate dance, and the odds of success will be even slimmer if the Taliban feel they are under no military pressure.

If the United States pulls out too quickly, any chance of a negotiated solution will collapse, and civil war is likely. That’s because the majority of Afghans, who don’t share the Taliban’s Pashtun ethnicity and fear the group, are already arming themselves. Afghanistan’s quarrelsome neighbors, such as India and Pakistan, will back different factions.

Down this road lies the Afghan chaos that enabled al-Qaida to thrive in the first place (and that would preclude our using Afghan bases to mount drone attacks in the future). To prevent such chaos, it is essential for a U.S. withdrawal to proceed slowly while U.S. regional diplomacy heats up.

Third, the transition: Congressional leaders, such as Sen. Carl Levin, D-Mich., who call for a more rapid transition from U.S. to Afghan security control are living in a dream world. Despite impressive U.S. training efforts ― which really ramped up only during the last 18 months ― the Afghan army and police are nowhere near ready for prime time.

Were political talks to begin, were the level of violence to decrease, the Afghan army might be able to take control of some of the country more quickly. If they are left alone too soon they are likely to crumble. This is probably not something the president wants to admit, but it is true.

And beyond all these security realities, there is one more point the president could have made, although doing so would have been tremendously impolitic: A swift U.S. exit won’t help Americans escape our economic mess.

Last week, the U.S. Conference of Mayors approved a resolution asking Congress to redirect billions being spent on bridges in Baghdad and Kandahar to Kansas City and Baltimore. The sad truth is that, even if all U.S. troops left Afghanistan tomorrow, those Pentagon funds wouldn’t be redirected to rebuilding U.S. infrastructure. (And Afghan reconstruction aid amounts to only $3 billion to $4 billion annually, compared with around $120 billion in military spending.)

The decision on how fast to leave Afghanistan must be based on our security needs; I think there is a strong argument for drawing down surely but slowly. I just wish the president had made the case in a way that was more compelling and clear.

By Trudy Rubin 

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. ― Ed.

(The Philadelphia Inquirer)

(McClatchy-Tribune Information Services)