That was the subtle message in the president’s response to a question on Afghanistan during his appearance with Russian president Dmitry Medvedev today.

Obama was careful not to frame July 2011 as a withdrawal date, but the beginning of a transition.

“We didn’t say we’d be switching off the lights and closing the door behind us. We said we’d begin a transition phase that would allow the Afghan government to take more and more responsibility,” he said.

That part isn’t so much news. But immediately after, Obama also said that at the end of this year his administration will undertake a second comprehensive review of its Afghanistan strategy. That point was also hit today by SecDef Gates and CJCS Adm. Mullen. Gates said that the administration would be looking to se if “by December we have enough evidence to demonstrate, if you will, the proof of concept” of the strategy.

By connecting the deadline talk with the strategic review talk, Obama and his national security principals are begging us to add the missing premise: if the review doesn’t show things proceeding smoothly in Afghanistan, the deadline could be pushed off, indefinitely. Of course, nobody in the administration wants to say that outright. But the hopes seems to be that it will be reassuring enough to signal it.