We can't quit in Afghanistan now

What that argument misses is the extent to which our presence in Afghanistan enables us to project power into Pakistan. It was from Afghanistan, after all, that the Navy SEALs took off to kill Osama bin Laden. If we pull back in Afghanistan, the Taliban will gain ground and the willingness of the Afghan government to provide us the bases we need will decline. That, in turn, will make it markedly more difficult to keep the pressure on Al Qaeda and prevent it from regenerating itself as it has in the past…

The administration can argue that even after we pull out all of the surge forces, we would have 70,000 troops in Afghanistan, considerably more than were there when President George W. Bush left office. But that is scant comfort because in 2009, the Taliban was on the verge of taking over southern Afghanistan. The surge has allowed coalition commanders to roll back Taliban gains in Kandahar and Helmand provinces. But the current progress is tentative and uncertain. Pull out a substantial number of our forces now and the success of the entire war effort is thrown into jeopardy.

Counterinsurgency is a manpower-intensive exercise.