For many of us who avoided the draft, the ensuing years brought with them not merely a measure of guilt, but also a deeper appreciation for the sacrifices of those who did serve. They gave rise to a new patriotism — one tinged with remorse, but also renewed recognition of the courage and grit of those who, no older than ourselves and no less eager to get on with their lives, had gone off to war.

I went into journalism, and one of my earliest assignments was to interview former Vietnam prisoners of war for articles about changing responses to interrogation and torture. I could not help thinking about what these P.O.W.s had endured while I read Horace and Catullus in the library. Over future assignments, I came to know better the caliber of men beside whom I might have fought.

Now 65, I am past the internal debate of whether it was cowardice or careerism or, most likely, some combination of the two that led to my decision not to serve. But that decision still imposes on me an added responsibility to pay homage to those who did serve — not to succumb to the insults of “baby killers” or the patronizing perception of volunteers as dupes, but to recognize that we are in their debt. I know of no one else of my generation who avoided the war who could speak the words that Mr. Trump did, who seems not to feel a pang of — call it what you will — conscience or guilt over unearned privilege or crass luck. We all have the sense that we, too, owe the country something of ourselves.

I do not begrudge Mr. Trump’s using deferments that many others also pursued. That would be the height of hypocrisy. But I am dumbstruck that someone who carries the weight of having seen others go off in his stead — friends, neighbors, classmates, teammates — could sneer at those who gave so much to the country. This is a threshold test of basic humanity and self-reflection that is, at least among those I know who did not go to war, heightened, not diminished.

The ignobility of the Vietnam era — the corruption and manipulation of the draft, the disproportionate numbers of the poor and minorities pressed into service, the ability of so much of the nation to carry on as if there were no war — created in many of us a special sense of purpose, a desire to make amends, to carry the weight of citizenship, albeit belatedly. Like so many other debts, this is one Mr. Trump evidently feels no obligation to repay.