Fouad Ajami describes the war in Afghanistan in very bleak terms. Karzai is even more of a scoundrel than many unseemly past American clients; and he's faced by an American administration particularly unsuited to deal with him.
Many years ago, when I was young and impressionable, there was this idea about how if America let the Communists overrun South Vietnam, there would be a domino effect and the whole region would fall, probably to be followed by worse. Then Kissinger let South Vietnam fall (Kissinger was not anybody's pansy), and lo and behold: there was no domino effect. (But there was a genocide in Cambodia, which was stopped eventually... by the Communist Vietnamese. The world is a complicated place).
Can the world afford America to retreat, effectively vanquished, from Afghanistan? No-one talks anymore about domino effects, but might there be one anyway? I don't know.