A sign of that ambivalence was the president’s announcement, in ordering 30,000 more troops into the fight, that he would begin pulling them out in July 2011. To many observers, especially in the region, it seemed that the president was undermining his own strategy from the outset. But this conditionality was apparently the only way Obama -- a president who grew up in the shadow of the Vietnam war -- felt comfortable with the decision.

The talk in Kabul and Islamabad 18 moths ago was that Obama would bail out in July 2011. But that hasn’t happened.

With tonight’s speech, the inflection point finally arrived. Obama announced a measured withdrawal of 10,000 of those surge troops this year -- more than military commanders might have wanted but far less than war critics have been demanding. In taking this course, he took ownership of the policy more decisively.

You could argue that, in choosing his own option, Obama fully became commander in chief of this war. He opted for what he thinks has worked: an aggressive counter-terrorism assault on al-Qaeda and its Afghan allies. And he implicitly rejected the more ambitious counter-insurgency goals of some of his commanders, who had hoped that by protecting the Afghan population, the United States could “take away the oxygen” from the Taliban. For all the gains in security in Helmand and Kandahar provinces, that COIN precept hasn’t proven out.

The most persuasive argument for the approach the president embraced tonight is that it will keep enough military pressure on Taliban forces to make them consider the wisdom of a negotiated settlement of the war. That’s the crucial strategic benefit of the president’s approach -- that it confounds the Taliban expectation that the United States would be gone by the end of this year. And to that extent, it makes the prospect of a negotiated settlement a little more plausible.