If you haven't read the NYT piece on Afghanistan today, you really owe it to yourself to. Rob Farley at Lawyers, Guns and Money has some thoughts on whether this retroactively de-legitimizes the invasion of Afghanistan in the first place.
I don't really know the answer to that question in my own head, but my suspicion that Afghanistan is going to end very badly for NATO makes me think it's time for us to leave. (The short version of my argument these days is that nobody has seriously considered enduring the costs that an actual success in Afghanistan would entail, so the forseeable future is bloody back-and-forths between us and the Taliban. Add martial and political incompetence to the mix, and, well...)
That said, I think there's two points I'd like to make in response to Rob's argument: one response to a specific point, and another more general argument.
First, the specific point. Rob writes:
It's certainly reasonable to argue that the Bush administration was too inept to successfully reconstruct Afghanistan, but that argument goes only so far. First, I was confidant at the time... that the US would receive significant international support during and after the invasion. No matter how badly the Bush administration performed, it was reasonable to believe that other countries would pick up much of the slack. This expectation has not been disappointed...
This, I think, underestimates the quantity and kind of incompetence the Bush administration has delivered in Afghanistan. The US troops under the ultimate command of George W. Bush make up most of the ISAF (NATO) forces in Afghanistan. Incompetent leadership of 17,000 (of 35,000 give-or-take) has an obvious determinative effect on the success of the international mission. No matter how competent 6,000 British are, they simply cannot undo the damage that the US Air Force is doing. Then you've got the reliance on high-technology weaponry as a substitute for manpower (vintage Rumsfeld, as if he'd never left) which is actively harmful to securing the loyalty of the Afghan people, or even the British army, as Matthew Yglesias pointed out recently.
Then there's the broader point which I think needs to be made: Rob writes that "Afghanistan isn't Iraq", in the context of arguing that the war hasn't failed. In the words of the Vietnamese officer, that's true, but it's also irrelevant. I fear that Iraq has become such a freakish horror-show that lesser, but still incredibly bad defeats seem somehow pleasant by comparison. But for those keeping track, the government of Afghanistan doesn't seem inherently more stable than that of Iraq, it's internal security is challenged by more quiet but far better organized threats, the Taliban and AQ can still set off explosives and kidnappings more or less at will throughout the country, and worst of all, Al Qaeda have gone from being protected by a barely-medieval failed state in 2001 to being protected by an industrially-armed nuclear power, nominally an ally, in 2007. And the self-inflicted stupidity that NATO's dealing with doesn't seem likely to stop any time soon -- NATO has agreed to use smaller bombs in its air strikes, a kind of comical gesture that totally fails to understand the real harm these things do to the war effort.
Whether this makes the invasion of Afghanistan retroactively a bad idea, I don't know. I supported the invasion in 2001 and for a long time after (declaring my bias, not appealing to seriousness) but the news from Afghanistan was worse in 2003 than 2002, worse in 2004 than in 2003, worse in 2005 than 2004, etc etc until today. There's some wishful thinking that the US could leave Iraq and transfer the freed troops to Afghanistan. I think the political impulse to remove troops from Iraq is likely to have a similar effect in Afghanistan -- "welcome home from Baghdad, now get on the plane to Kabul" doesn't seem like it would play well in Peoria.
Fundamentally, I don't think any western capital, including D.C., is really convinced anymore that Afghanistan's fate is a matter of vital importance. If we were, we'd have changed our policies a long time ago. But even the nominally pro-war party in Canada doesn't think the situation is serious enough to merit postponing precious, precious tax cuts.