Here’s how an Obama official described it earlier today to reporters:
The other key task for the military, this additional 30,000 over the coming months, is to train and partner with the Afghan security forces to accelerate their development. The broad aim here is to open a new window of opportunity for Afghanistan and to create conditions to begin to transfer to Afghan responsibility by a date which the President will specify in his speech.
So let me just cover that again, because this is a point — this is a point which can easily be confused. What the President will talk about tonight is a date by which he has given the mission that we will begin to transfer our lead responsibility — that is, the U.S. and NATO lead responsibilities from that operation — to Afghan counterparts. He will not, however, tonight specify the end of that transition process, nor will he specify the pace at which it will proceed. Those variables — pace and end — will be dictated by conditions on the ground.