Afghanistan - stick or twist?

Should we pull out of Afghanistan? Is America doomed either way?

A conversation with the Major suggests yes. He posits this theory: that by pulling out, America will once again demonstrate its inability to win, even against a seemingly less substantial force (c.f. Vietnam). Everyone will think they are losers, despite their manpower on the ground in troop terms. Result: America is doomed as a superpower.

They stay in - troops are killed, innocent civilians are killed, but they do not feel able to pull out for the reasons demonstrated above. All their economic power goes towards keeping the war going; in the meantime, Russia and China creep up and beat them to the top in the superpower stakes. Result: America is doomed as a superpower.

It's simplistic, but he has a point. What is the solution to Afghanistan?