Nate Fick, whom I saluted here, had an op-ed in the NYT last week on the decision by the Obama administration to announce a deadline for withdrawal, here.  His conclusion:

Announcing the timeline was risky, and it could turn out to be our undoing. The president delivered two intertwined messages in his speech at West Point outlining his Afghan policy: one to his American audience (“I see the way out of this war”), and one to the people of Afghanistan and Pakistan, including the Taliban (“I’m in to win”). The danger of dual messages, of course, is that each may find the other audience, with Americans hearing over-commitment and Afghans hearing abandonment.
The only way to reassure both is to show demonstrable progress on the ground.  A credible declaration of American limits may, paradoxically, be the needed catalyst.”