“He’s not a war hero,” Donald Trump said two years ago, speaking at a Republican Party candidates’ forum in Iowa. “He’s a war hero because he was captured. I like people who weren’t captured.” Trump’s insult to Senator John McCain—and, by extension, to every American P.O.W.—drew a gasp of rebuke from across the political spectrum. The initial indignation, however, did not last; in hindsight, it seems one of the final instances of a broad cultural unity that now seems lost to this country forever.

The reason for the universal, if brief, repugnance was obvious: McCain’s conduct during nearly six years in a North Vietnamese prison, the infamous Hanoi Hilton, had become the stuff of legend. In 1968, less than a year after his Navy bomber was shot down, the imprisoned McCain was abruptly offered unconditional release by the North Vietnamese, perhaps because his father had just been named the commander of U.S. forces in the Pacific. McCain was still badly crippled from his crash and the poor medical treatment that followed, yet he adhered to the P.O.W. code of honor and refused to be repatriated ahead of American prisoners who had been in captivity longer than he. His refusal was adamant. His guard told him, “Now, McCain, it will be very bad for you.” He was tortured for his defiance, and ultimately spent more than two years in solitary confinement. The abuse, combined with the after-effects of his injuries, left him physically marked. He could have avoided it all, but out of loyalty and—one has to name it—love for his comrades, he chose not to.

One of the peculiarities of Trump’s constant outrages is the way in which, every now and then, they accidentally bring to the surface deep matters of meaning and morality. In fact, the future President was partly correct in Iowa, though not in the way he supposed; McCain never considered himself a war hero. More than twenty years ago, I interviewed him for the magazine, and I remember as if it were yesterday the anguish that came into his face when he described the worst part of his imprisonment. A son and grandson of Navy admirals, he was raised with a steely sense of martial honor. As he experienced it, he grotesquely betrayed that honor when, under the pressures of torture, he broke. He abjectly signed a “confession” declaring him a “black criminal” and an “air pirate.” To himself, after that, McCain was a traitor to his nation and his family. Returned to his cell guilt-ridden and despondent, he came close to suicide. This misery outweighed any possible sense of valor he might have derived from the stalwart resistance that actually defined his time in captivity, and that others would simplistically see as grand heroism.

What McCain did in refusing release from the Hanoi Hilton ennobled him, but his survival of the moral collapse that his captors forced on him was, arguably, the precondition of the further heroic work he accomplished years later. The memory of the Vietnam War, that self-inflicted American wound, festered for decades after the nominal end of hostilities, in 1975. The United States, nursing its trauma, imagined itself as the war’s victim, and punished the victorious but impoverished Vietnamese with a crippling economic embargo. Justifying this vengeful spirit and exacerbating it was the false belief that dozens, or perhaps hundreds, of Americans were still being held in secret P.O.W. camps in the jungles of Southeast Asia—a grim fiction that was promoted by the “Rambo” films, jingoists such as Ross Perot, and politicians including Ronald Reagan and Bob Dole. Thousands of bereft family members were encouraged to anticipate the eventual return of loved ones who were, in fact, long dead. Their icon was the black P.O.W./M.I.A. flag, with the silhouette of a man beneath a guard tower.

It took the Senate Select Committee on P.O.W./M.I.A. Affairs, chaired by John Kerry, to lay the myth to rest, in 1993. The group’s difficult finding—that there was no evidence that any Americans had been held back in Vietnamese prisons—was agreed to unanimously by all members, across the political divide, from far right to far left. It was a truly bipartisan outcome, one of those increasingly infrequent moments in which facts vanquished ideology on Capitol Hill. No one was more central to that blazingly controversial effort than John McCain. By dismantling the last pillar of American contempt for Vietnam, McCain, in partnership with Kerry, led the way to the lifting of the embargo, the diplomatic recognition of Vietnam, and the true end of the war. The friendship that developed between the famously antiwar Kerry, whose protests had been despised by the prisoners in Hanoi, and the lionized patriot McCain became a hopeful example of American reconciliation. McCain’s capacity for magnanimity was grounded in his refusal to regard himself as morally superior. That he was no hero to himself was what made him the hero America actually needed.

Alas, the golden moment of rational bipartisanship did not last. Though it laid the groundwork for prosperity in Vietnam, it was soon undermined in America by a sequence of political jolts—the Gingrich revolution, the Clinton scandals, the politicization of the Supreme Court with Bush v. Gore, and the fake-news swift-boating of Kerry himself. After 9/11 and the Bush wars, in particular, the nation’s old wound opened wide again. (Indeed, the black P.O.W./M.I.A. flag, emblem of U.S. victimhood, still flies everywhere.) McCain, in the grip of inherited martial fervor, was a cheerleader for Bush’s misadventures, and finally he, too, was undone by the renewed collapse of American common sense and common decency. Sarah Palin, the running mate he chose in his 2008 bid for the Presidency, turned out to be the drum major marching just ahead of Trump’s parade.

There is a painful irony in McCain’s having served, by the insult done to him at that Iowa candidates’ forum, as one of the pivot points on which the national narrative has turned. He showed that Trump could mock self-sacrifice, could demean honor, and blithely get away with it, even among those who should most have found it unforgivable. Now that the Arizona senator has received the heartbreaking news of his brain-cancer diagnosis, recalling Ted Kennedy and Beau Biden, it is urgently important that Trump not have the last word. McCain’s admirable loyalty to his fellow-prisoners—and, by extension, to the nation—was in no way undone, as he himself feared, by his having been overwhelmed by torture. On the contrary, being stripped in captivity of moral self-righteousness as well as physical health prepared him to emerge at the crucial moment as a figure of American redemption, of aspirational nobility—even if the nation lately falls far short of the standards set fifty and twenty years ago by Senator John McCain.