One of the oddest — indeed, surreal — encounters around the war in Afghanistan has to be a telephone call this past July 27. On one end of the line was historian Stanley Karnow, author of Vietnam: A History. On the other, State Department special envoy Richard Holbrooke and the U.S. military commander in Afghanistan, General Stanley McChrystal. The question: How can Washington avoid the kind of defeat it suffered in Southeast Asia 40 years ago?