There’s considerable concern too about the legitimacy of the regime after elections that were, to put it mildly, flawed.
The Washington Post has an interesting exchange of views on its op-ed page. The proponents of remaining in Afghanistan can define failure but they can’t define success — at least not concretely.
Some make a moral argument that we owe it to the Afghans, that allowing failure would be wrong. I think this runs up against the cost question. McChyrstal argues for troops getting out of vehicles more — this is necessary to reduce civilian casualties — but doing so will increase our casualties. Popular opinion is going to stiffen in opposition to this war if that should happen. To go that route is to plan for failure because we’ll turn back before we reach its distant, elusive goal.