The author of “The Mirror Test” is recognizably that figure. Weston chose to spend three years in the Mad Max inferno of Falluja, much of it in a tiny post where he was the only civilian embedded with two dozen Marines. He had a front-row seat for the slaughter that ensued when American forces were ordered, in 2004, to retake the city from insurgents, obliterating much of it in the process. Weston essentially assigned himself the job of finding local partners willing to work with Americans to rebuild Falluja in exchange for endless stacks of American money, and, even more urgently, to function as the city’s informal government.

That, as Weston knew, is how counterinsurgency wars are won — not by killing bad guys but by defeating their cause in the minds of ordinary citizens. Counterinsurgency is a battle for political legitimacy — and the insurgents fought back remorselessly. Virtually every Iraqi courageous or crazy enough to join Weston’s cause was murdered. But Weston also describes America’s unwitting connivance with its enemies. In the fall of 2005, United States special forces troops in their ubiquitous Black Hawk helicopters swooped in to kidnap a young Falluja woman, Sara al-Jumaili, thought to be the girlfriend of an insurgent kingpin. They had not, of course, asked anyone about the political consequences of doing so. All Falluja assumed Sara had been seized in order to be raped at an American base. The city was up in arms. In a desperate act that he describes as insubordination, Weston wrote to George Casey, the commanding officer in Iraq: “It is 1651 [4:51 p.m.] on Thursday. If Sara al-Jumaili is not released before Friday prayers, Marines and civilians will die.”

Sara was released, but too late to prevent a disaster. Sheikh Hamza, Falluja’s revered grand mufti and Weston’s most prized recruit to local governance, had refused to publicly denounce the Americans, knowing that doing so would unleash a spasm of violence. One month later, Sheikh Hamza was gunned down outside his mosque. All of Weston’s efforts had been for naught. He was enraged — at political leaders in Washington, diplomats in Baghdad, special forces commanders in Tampa. Although counterinsurgency strategy in Iraq — the surge — is widely considered a success, Weston shows us, in miniature, how the military imperative of killing terrorists consistently trumped the political one of empowering local actors. Today, of course, Iraq has a dysfunctional Shia-dominated government threatened by the Sunni terrorists of ISIS.

“The Mirror Test” is a memoir, not a policy paper. Weston writes of the consuming guilt he felt after he authorized a mission that led to the death of 31 Marines in a helicopter crash. Large portions of the book are devoted to his travels back home, visiting the grave sites in a search for expiation, or working with wounded vets. Here Weston seems to be fulfilling an obligation to himself rather than to the reader. The emotional core of “The Mirror Test” is Weston’s profound love for the Marines, whose stoic warrior culture and bottomless commitment to one another he embraces. This reverence, however, blurs the book’s intellectual outlines, since Weston’s buddies don’t share either his horror of the wars or his commitment to putting politics and diplomacy first.