If we were able to capture Osama Bin Laden, and either have him tried in a U.S. Court, or Get confirmation of his death at U.S. hands, A lot of America's credibility might be reastablished.
Of course, we would have to time it with something like, oh, a sizeable U.S. troop withdrawal...how that would work with the current situation though, might be catastrophic. I would give the Iraqi government long odds on survival, and it would probably wind up getting assimilated by Iran, with a puppet extremist government(And a probable genocidal kind of ethnic strife.)