John McCain’s most courageous moment arguably did not come when he was near death as a prisoner of war in North Vietnam. He was then frail and feverish, with two broken arms, a broken leg, a shattered knee and bayonet wounds, yet still resisting his captors even though the consequence was more beatings.

Rather, his bravest moment may have come in the winter of 2007-08 as he sought the Republican nomination for president. In polls, two-thirds of GOP voters then supported torture, yet McCain led a battle against Vice President Dick Cheney on the issue and repeatedly denounced torture.

Waterboarding “is a horrible torture technique,” McCain told Iowa voters. “This is a terrible and odious practice.”

During a debate, McCain called extreme interrogation a “violation of existing law” as well as of the Geneva Convention. “I know how evil this enemy is,” McCain told an audience in Iowa, but he added, “This is really fundamentally about what kind of nation the United States of America is.”

This was the last thing voters wanted to hear. Even many Democrats were then reluctant to denounce torture, and news organizations often refrained from using the word “torture” to describe waterboarding. (The New York Times news pages did not adopt the word “torture” for such practices until 2014.)

Yet here was a Republican candidate back in 2007 repeatedly rebuking voters on waterboarding and standing up for the rights of suspected terrorists from al-Qaida. That’s what political courage and moral leadership look like, and why we can all learn something from McCain.

I disagreed with John McCain on countless issues, from his support for the Iraq War and the 2017 tax bill to his 83 percent voting record in sync with President Donald Trump. He was a conservative and I’m a liberal, so he frequently infuriated me (Sarah Palin for veep, really?!). But for all our disagreements, I deeply admired his guts, passion and determination to follow his moral code. His death leaves a great emptiness in Washington.

It is not that McCain was courageous at every moment. But even when he pandered, he was the world’s worst panderer — so obviously guilty and uncomfortable as he trolled for votes that he convinced nobody and was always penitent afterward.

As a presidential candidate in 2000 competing for votes in the South, he described the Confederate flag as “a symbol of heritage.” Later, he apologized and explained, “I feared that if I answered honestly I could not win the South Carolina primary, so I chose to compromise my principles.”

In the courage-free zone known as Congress, McCain showed that principle and politics can mix at the highest levels. And if it wasn’t often enough, well, he would be the first to admit it. Characteristically, he described his pick of Palin as “another mistake that I made.”

At his best, he was in a league of his own. Watch the video from the 2008 campaign of a rally where a man says “we’re scared of an Obama presidency.” McCain challenges the man, saying of Obama: “He is a decent person and a person that you do not have to be scared as president of the United States.”

Then a woman speaks up and says she can’t trust Obama because he’s an Arab.

“No, ma’am,” McCain says. “He’s a decent family man, citizen that I just happen to have disagreements with on fundamental issues, and that’s what this campaign is all about.”

There was, of course, another side to McCain, for he was a complex, contradictory figure. He betrayed his first wife, Carol, who had raised his three children by herself while he was in Vietnamese prisons. After returning home, while still living with Carol, he began pursuing his current wife, Cindy, who was young, beautiful and rich.

When he married Cindy, his children were angry (only at him; no one blamed Cindy) and none attended the wedding, but everyone forgave him soon enough. Not least because John McCain was always his own severest critic. He was contrite, and he blamed himself rather than others.

That moral compass is what distinguished McCain, more than his war record, his wicked wit, his tireless travel schedule and his familiarity with far corners of the globe. (I happened to be in Moldova once when he visited. The difference was that he had been in Moldova so often, even though voters could never have found it on a map, that he seemed to know it like Phoenix.) Above all, what set McCain apart was that he was guided not by a weather vane but by deeply felt principles.

Nicholas Kristof is a columnist for The New York Times.