The question we face, on the first anniversary of the surge, is no longer whether the president’s decision a year ago was the right one, or if the counterinsurgency strategy developed by Gen. Petraeus is working. It is. The question now is where we go from here to sustain the progress we have achieved — and in particular, how soon can more of our troops come home, based on the success of the surge. Gen. Petraeus has already announced that five “surge” brigades will be withdrawn by mid-July. The process is now underway. The Pentagon has also announced that it is conducting a series of internal reviews to examine whether and when additional troops can be withdrawn — with Gen. Petraeus, the Joint Chiefs of Staff and U.S. Central Command each asked to offer their own analysis. As the president awaits these recommendations, it is important for the rest of us to keep some realities in mind. First, it is unknown whether the security gains we have achieved with the surge can be sustained — and deepened — after we have drawn down to 15 brigades. Until we know with certainty that we can keep al Qaeda on the run with 15 brigades, it would be a mistake to commit ourselves preemptively to a drawdown below that number. As the surge should have taught us by now, troop numbers matter in Iraq. We should adjust those numbers based on conditions on the ground and the recommendations of our commanders in Iraq — first and foremost, Gen. Petraeus, who above all others has proven that he knows how to steer this war to a successful outcome.