“My greatest fear,” General Raymond Odierno, the then commanding general of U.S. forces in Iraq, told me in early 2010, “is that we stabilize Iraq, then hand it over to the Iranians in our rush to the exit.” General O (as he is known), had recently watched the 2007 movie Charlie Wilson’s War, which recounts how U.S. interest in Afghanistan ceased once the mujahedeen defeated the Soviet Army in 1989 and drove them out. Now, he had a premonition that the same could happen in Iraq. “I’ve invested too much here,” he said, “to simply walk away and let that...