No matter where my colleagues came down in 2003 about the centrality of Iraq to the war on terror, there can simply be no debate that our efforts in Iraq today are critical to the wider struggle against violent Islamic extremism. Already, the terrorists are emboldened, excited that America is talking not about winning in Iraq, but is rather debating when we should lose. Last week, Ayman al-Zawahiri, al-Qaeda’s deputy chief, said that the United States is merely delaying our “inevitable” defeat in Iraq, and that “the Mujahideen of Islam in Iraq of the caliphate and jihad are advancing with...