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When I was a cadet in the Army ROTC during summer training at Fort Bragg, I purchased at the post exchange a garish T-shirt that said Kill a Commie for Mommie. It had all kinds of appalling pictures on it. I did not have the courage, however, to wear it in Harvard Square (or anywhere else, for that matter), and it soon vanished.

This uncomfortable memory came to mind as I reflected on President Donald Trump’s latest tussle with the Department of Defense, over the pardon of two Army officers convicted of war crimes and his intervention on behalf of a Navy SEAL acquitted of a crime but nonetheless disgraced for posing with the corpse of a fallen enemy and holding a reenlistment ceremony near it. Trump’s view—and that of many others—seems to be that war is war, close combat is grisly business, and those who do it need a kind of brutal aggression that leads to these kinds of things. They can be forgiven the occasional bad stuff.

It’s been worse. In May 1944, the picture of the week in Life magazine was a young woman gazing at the skull, supposedly of a Japanese soldier, that her boyfriend had sent her from overseas. He and a dozen of his friends had autographed it, and she reportedly nicknamed it Tojo. In the field itself, it was not unheard of for American troops to take ears from corpses, or to put the occasional head on a stake.

There are two schools of thought here: Trump’s view, which, if it’s not quite “boys will be boys,” is understanding and in large measure indulgent, and a kind of fastidiousness that goes in the other direction altogether. In February 2005, then-three-star General Jim Mattis said, “You go into Afghanistan, you got guys who slap women around for five years because they didn’t wear a veil. You know, guys like that ain’t got no manhood left anyway. So it’s a hell of a lot of fun to shoot them.” There was a fuss, and he got a reprimand for not choosing his words more carefully. It probably would have been worse for him in Barack Obama’s administration than it was in George W. Bush’s.

The truth about Mattis, of course, is that in practice he believes in erring on the side of restraint, cautioning his marines not to take a shot when civilians are likely to get hit, and gently talking a newly elected Trump out of his belief in the utility of torture. But his unvarnished remarks, like my juvenile T-shirt (complete with a skull with a red star on its forehead, as I remember), indicate the dangerous lines up to which militaries must go, but across which they must not pass.

War, and close combat above all, requires the desire to destroy the enemy, and destruction here is all about shredding human bodies with bombs, bullets, and, even in this day and age, edged weapons. It is about killing. Decent people recoil from it; a liberal society, even one accustomed to gun violence on a large scale, will often try to avoid it, but there it is. And to build the necessary aggression, things have to be different in war than in peace, and soldiers have to have their blood up.

As ever, Shakespeare can guide us through this. In Henry V, the bard’s perfect king masses his troops before the French city of Harfleur, and as he leads them “once more unto the breach,” he says:

In peace there’s nothing so becomes a man

As modest stillness and humility;

But when the blast of war blows in our ears,

Then imitate the action of the tiger

Stiffen the sinews, conjure up the blood

Disguise fair nature with hard-favored rage.

And so soldiers do. Henry rouses them by appealing to their pride, their lineage, their patriotism, and their prowess. He will lead them in person; he is the noble warrior even if he is not fighting for a noble cause.

But it does not end there, because the city is not taken by that assault. Instead, Henry delivers a terrifying speech to the governor of Harfleur and his people, telling them what will befall them if they do not surrender on the spot:

The gates of mercy shall be all shut up,

And the fleshed soldier, rough and hard of heart,

In liberty of bloody hand shall range

With conscience wide as hell, mowing like grass

Your fresh fair virgins and your flow’ring infants.

He lays it on thick, returning to the theme of rape, describing what it will be like when “your pure maidens fall into the hand / Of hot and forcing violation.”

Those who would like to forgive or excuse Henry suggest that this is mere psychological warfare—he does not really mean it; he’s just playing a mind game with the holders of a stubborn fortress. But the telling line is this:

What rein can hold licentious wickedness

When down the hill he holds his fierce career?

Henry knows, and the men of Harfleur know, that this is true—and here is the point, indeed. Once you cross a line, you do not stop, and you massacre unarmed civilians, and you torture prisoners, and you mutilate the corpses and play with the pieces of dead enemies. And at that point, you have damaged, if not lost, your soul.

American military leaders understand this; they know that once license is given, cruelty and murder roll down the hill, and become impossible to stop. That is why there is military law, and persnickety Judge Advocate General’s Corps officers who bring charges; that is why it is the generals who blow the whistle; that is why when deeds of the kind described in these courts-martial are tried by a jury of military peers, the accused are often convicted.

And the restraints on such conduct go further: Knowledge of this danger is one of the reasons the military is finicky about discipline—not just because its power is so great, but because the possibility of moral chaos is ever present. It is the discipline ingrained during months and years of training that enables a new second lieutenant to prevent a war crime with one sharp order. The United States military keeps itself in line by planting a thick hedge of norms and values, and if it ever were to lose it, woe betide the military, and woe betide the country.

As is so often the case, the issue here is not just the president and his personal beliefs and whims, or political opportunism. It is, rather, a national question of where a society draws the line regarding what it expects of its armed servants. Individuals may differ on where that line should be drawn, but without it, licentious wickedness will have its day.

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