The coming year will put this political calculation to the test. Obama’s left flank is increasingly agitated with loose talk about primary challenges, yet he has few opportunities to appease them on domestic policy. Only moderate policies have a chance of passing the Republican House, so anything done on the domestic side will likely further antagonize Obama’s left-wing base. They will naturally turn to national security, where Obama enjoys more freedom of action, for compensation.

Come August, the contradictions in White House messaging about the Afghanistan timeline will be unspinnable. Either the timeline will start a rapid rush to the exit as the left base wants or it will be the gradual, conditions-based withdrawal inching towards a distant 2014 deadline (followed by a long-term strategic partnership) that General Petraeus and moderates in the war cabinet have indicated.

If Obama opts for the former, then Republican support for the war will likely quickly diminish. People who supported a war they thought they could win will not want to be caught as the last one supporting a losing effort. If Obama opts for the latter, then any remaining left-leaning props undergirding public support for the Afghanistan war will likely collapse altogether. The timeline straddle bought muted Democratic criticism, but the mutes will be off once the straddle is abandoned.