JOHN MCCAIN’S sense of obligation to his country was shaped by a long family history of military service that included the contributions of two four-star admirals: his father and paternal grandfather. It was tested to the utmost by five years of cruel confinement and torture in a North Vietnamese prison — an ordeal from which he emerged to spend many years in public office and national prominence.

But it may be that the most important episode of his life — in terms of giving him an understanding of what Americans owe to each another — was one that occurred a few months before he was brought down over Hanoi. In late July 1967, he was in the cockpit of his A-4 Skyhawk fighter jet on the deck of the USS Forrestal when a rocket was accidentally launched across the deck, wreaking havoc on the ship. Mr. McCain, then a lieutenant commander, escaped the inferno, his flight suit in flames. One hundred and thirty-four lives were lost in the explosion and fire.

“After a short while,” he wrote in an affecting passage in his memoir, “I went to sick bay to have my burns and shrapnel wounds treated. There I found a horrible scene of many men burned beyond saving, grasping the last moments of life. . . . Someone called my name, a kid, anonymous to me because the fire had burned off all his identifying features. He asked me if a pilot in our squadron was okay. I replied that he was. The young man said, ‘Thank God,’ and died. I left the sick bay unable to keep my composure. . . . Men sacrificed their lives for one another and for their ship. Many of them were only eighteen and nineteen years old.”

In that book, “Faith of My Fathers: A Family Memoir,” Mr. McCain spoke frankly of his imperfections: “I have spent much of my life choosing my own attitude, often carelessly, often for no better reason than to indulge a conceit. At other times, I chose my own way with good cause and to good effect. . . . When I chose well I did so to keep a balance in my life — a balance between pride and regret, between liberty and honor.”

American politics was badly out of balance during Mr. McCain’s final years, and while he angered some and made his share of mistakes, he accomplished as much as any politician of his time toward restoring some sense of equilibrium — and of truth, honor and integrity — to the governing of a nation that he served well and courageously in war and in peace. He became a dominant figure in the Senate through willpower, persistence and determination, because he commanded the respect due one who has sacrificed much for his country, and because, more often than most these days, he knew what he believed and stuck to it.

Mr. McCain represented a conservative state, and much of his record reflected that fact. He did some things in the interest of getting elected that he later regretted and renounced, such as a vote early in his Arizona political career against the creation of a national holiday honoring the Rev. Martin Luther King Jr., and his failure in 2000 to take a stand against the display of the Confederate flag in South Carolina at a time when he was running in a presidential primary there. After the primary, he returned to South Carolina and said of his evasiveness on the flag issue: “I feared that if I answered honestly, I could not win the South Carolina primary. So I chose to compromise my principles. I broke my promise to always tell the truth. . . . Honesty is easy after the fact when my own interests are no longer involved.” He also let politics push him to choose Sarah Palin, the untested Alaska governor, as his presidential running mate in 2008 when he would have preferred the more-qualified Connecticut senator, Joseph I. Lieberman.

We disagreed with Mr. McCain on various matters over the years, but when we did so, it was more with a sense of disappointment than of anger. He was such a respected figure that his views had credibility even among many who strongly opposed them. And on some of the great issues of his time — campaign finance reform, immigration, human rights, promotion of democracy, treatment of prisoners, national defense and deterrence of foreign aggression — Mr. McCain was a courageous and principled leader. With his climactic vote in the summer of 2017 against a health-care bill that he thought bad for the country, he made a dramatic plea for cooperation and mutual respect in Congress. It was a message that should be heeded, especially by those in his party who seem to have come unmoored from their conservative principles by the faux-populist exploits of President Trump. Mr. McCain, on numerous occasions, rose above party politics to pursue what he honestly saw as the national interest, and he accomplished a great deal. The country has lost an irreplaceable asset.