The news from Afghanistan all year has been dispiriting, and the last few weeks have been especially tough in terms of the violence. Yet most foreign and Afghan officials and officers who I encountered on a recent weeklong visit sponsored by the U.S. military are guardedly optimistic about our prospects.

How can this be so? Sure, we have all heard the theoretical explanation of how this war, like any counterinsurgency, could be won through a "clear, hold, and build" process of pushing extremists out of population centers and then helping establish a legitimate Afghan government in their place. But can it really work in tribal, underdeveloped Afghanistan?