At a moment of salutes and farewells, this may be John McCain’s greatest moment

Shot down over Hanoi and imprisoned for more than five years, two of them in solitary confinement. Turned down early release because fellow prisoners were still in captivity. Elected to the United States House of Representatives and then served in the Senate for nearly a third of a century. Ran for president twice, won the 2008 Republican presidential nomination, lost the general election but praised Barack Obama’s ascendancy as a signal American moment. Repeatedly earned the enmity of his GOP allies and the favour of his Democratic rivals.

But for all that — for his profile as both icon and iconoclast, for his reputation for both valour and vanity — this may be the greatest John McCain moment.

As he continues to battle glioblastoma brain tumours while resting in his mountain hideaway in Arizona — where his support for immigrants is out of step with the state’s impatience with illegal immigration, where his opposition to President Donald J. Trump is out of sync with the Manhattan billionaire’s decisive 2016 victory in the state — Mr. McCain is, in a phrase redolent of the romance of the old American West, dying with his boots on.

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But as he lay dying, he remains an avatar for what Abraham Lincoln called ‘’the better angels’’ of the American character and, improbably but indisputably, he remains at the centre of American life, an apt coda for a man whose family contributed four generations, from Guadalcanal to the Iraq war, to the U.S. Navy, and whose service on Capitol Hill spanned the arc from Mr. Carter to Mr. Trump.

Just last week, for example, Mr. McCain, who was tortured in the Hỏa Lò Prison in Hanoi, came out in opposition to the President’s nomination of Gina Haspel, who oversaw torture interrogation techniques after the Sept. 11 terrorist attacks, to head the CIA. That prompted a White House official to spawn a collateral contretemps by dismissing Mr. McCain’s comments because ‘’he’s dying anyway.’’ The White House did not condemn the abasement, which was especially stinging because Mr. Trump had earlier disparaged the Arizona Republican by saying, ’’He’s not a war hero. He’s a war hero because he was captured. I like people that weren’t captured.”

Even so, last week’s episode captured the essence of Mr. McCain: his willingness, even in mortal peril, to stand up rather than to step aside, even when it jeopardizes the politics or undermines the policies of the Republican Party he has embraced since he was the protege of another GOP maverick from Arizona with a strong military heritage, Senator Barry Goldwater.

A warrior by inheritance, instinct and inclination, Mr. McCain is a party warrior with a recessive gene for nonpartisanship.

It was by crossing party lines that he won his signature legislative victory, an overhaul of the U.S. campaign-finance laws. In 2013, he voted to support the policies of his 2008 rival Barack Obama more than half the time. Nine years earlier, a fellow Vietnam veteran, Democratic presidential nominee John Kerry, seriously contemplated selecting the Republican Mr. McCain as his running mate.

Mr. McCain cherished his association with the Republican Party but never was a slave to it, which is perhaps why he was honoured by both the Eisenhower Institute and the John F. Kennedy Presidential Library and Museum, which presented him with its coveted Profiles in Courage Award 19 years ago this month.

Mr. McCain, to be sure, was not always a citadel of civility;he has a temper and he harbours a weakness for the cutting aside, such as one that disparaged the physical appearance of Chelsea Clinton. And yet from the start he was a spokesman for civil discourse in politics and, in The Restless Wave, his memoir to be published next week, when he may not be alive to savour the moment, he wrote:

‘“Whether we think each other right or wrong in our views on the issues of the day, we owe each other our respect, as long as our character merits respect, and as long as we share, for all our differences, for all the rancorous debates that enliven and sometimes demean our politics, a mutual devotion to the ideals our nation was conceived to uphold, that all are created equal, and liberty and equal justice are the natural rights of all.’’

Mr. McCain’s last days have been full of reflection, not recrimination, and his memoir, a stirring meditation by a man who wrote that, ‘’I served a purpose greater than my own pleasure or advantage,’’ has spawned perhaps the greatest McCain moment in the United States, a surge of contemplation on national purpose and personal rectitude.

Part of it came as a parting shot at Mr. Trump and what Mr. McCain describes as the President’s ‘’apparent lack of appreciation for the importance of our values...and for the understanding that simple human decency is as essential to the souls of nations as it is to the souls of people.’’

But as he departs, Mr. McCain was less interested in settling scores than in setting Americans to thinking about issues bigger than those on the Sunday cable shows or the newspaper front page.

‘’Our time is our time,’’ Mr. McCain wrote in the fifth page of his final testament. ‘’It’s up to us to make the most of it, make it amount to more than the sum of our days.’’ These days, when we live with the sum of our fears, that thought — and the challenge inherent in it — may be the greatest gift of Mr. McCain’s greatest moment.