Staying The Course in Afghanistan

Bret Stephens busts George Will's chops for wanting to cut and run in Afghanistan (very bad news if we leave now, basically). I agree with him, but I'd also like to know what victory means there; our goals seem less and less clear. I note his concluding graf:
The alternative is a winding and bloody struggle to defend and improve a hapless and often corrupt government in a godforsaken land of often (though by no means pervasively) ungrateful people. This is not the noblest fight, and no sane nation would wage it by choice. But we did not choose it and, if we keep our nerve, we can win it.