Quick hit: if US pulls back in Afghanistan what does that say about Gates' Pentagon procurement changes? Much of what the budget changes dictate concerns Gates' admonition 'fund what's suitable for the wars we're fighting now, not may fight in some future' - failure to fund the F-22 for instance is a reflection of that. But if we're not going to fight the war we're fighting now, Afghanistan, then how much sense does the policy defined by Gates' budget make?
Not that Gates' recommendations are all about COIN - but the fact remains that insurgency tactics have been used quite effectively in the wars Gates is referencing and so COIN is implied - therefore, if we're incapable or unwilling to commit to such a conflict now, it certainly seems reasonable to ask what that says about the Gates doctrine.
