That may be the real reason the United States keeps spending so heavily in Afghanistan. The Pentagon is terrified of a repeat of 1975, when panicked South Vietnamese fled Saigon as Americans pulled out and North Vietnamese forces advanced on the city. The United States military did not truly begin to recover from that humiliation until its victory in the Persian Gulf war of 1991. An abrupt withdrawal from Afghanistan could conceivably provide a new symbol of the decline in American hard power.

There is also the fear that an Afghanistan in chaos could once again provide a haven for an international terrorist group determined to perpetrate another Sept. 11-scale attack. Of course, Yemen, Somalia and a number of other places could also provide the setting for that.

The point is, we remain in Afghanistan out of fear of even worse outcomes, rather than in the expectation of better ones. Washington now merely hopes that Mr. Khalilzad, an experienced diplomat born in Afghanistan, can deliver a decent interval of stability.