When John McCain revealed in July that he'd been diagnosed with glioblastoma—the same aggressive form of brain cancer that killed his friend Ted Kennedy—the news seemed of a piece with all of the other dismal political headlines of the year. But in the midst of surgery and radiation and chemo, the Arizona senator somehow emerged as perhaps the most consequential man in Washington, casting the deciding "no" vote on the Obamacare repeal; urging his fellow senators, Republicans and Democrats alike, to do better; and serving as a thorn in the side of Donald Trump. It wasn't that the war-hero senator, now 81, abandoned partisanship altogether (his decision in recent weeks to back Republican tax cuts proves that point). But on more than a few occasions, McCain's principled stands—made in the face of adversity—provided overdue example of just the sort of leadership that could help repair our broken politics. We spoke to McCain in October about the tumultuous year in politics, his health, and about what he's still eager to achieve.

GQ: How has Washington, D.C., changed since you arrived 30 or so years ago?

John McCain: You know, as we grow older, we forget the rough spots and we only remember the good times. That's just human nature, as you know. But having said that, the Senate was a much more congenial place than it is today. That seems to be missing now. And there's clearly a polarization that's taking place that outside forces are effecting. For example, declaring a jihad against certain senators because they weren't in line with certain people's beliefs. In other words, disagreements, sometimes strong disagreements, but it's much more intense.

If you were to mentor someone new to politics, what would you tell them? What would you want them to know about Washington, about Congress, about public life?

I would talk to them about two things: Do the right thing. And second, develop relationships. You know, one of the great joys of my life was, after I was elected to the House, Mo Udall took me under his wing—liberal Democrat, but totally together on Arizona issues, he and I. He was one of the most entertaining, funny, but thoughtful people that I have ever known. He and Ted Kennedy both told me the same thing: If a joke is funny, it's worth telling again and again and again. I loved Mo; he couldn't have been kinder to me.

So what would I say to a new member of Congress? I'd say, "Look at what Mo did." He had an incredible impact, and he always had me join in. You know, he'd call me over and say, "Okay, here's what we're gonna do. What do you think?" I'd say, "I'm with you." You're not going to get things accomplished purely on a party-line basis. We are seeing graphic examples of that now.

Your family has been in public service for a long time. Of course, many people think of our current political moment as very fraught, but how do you view it, in the scope of what your family has seen?

You know, Henry Louis Gates does a television show where he traces people's ancestry, and they traced mine all the way back to Charlemagne. And my great-great-great-great-whatever-it-is was a colonel on General Washington's staff. My family has been involved in literally every conflict, every conflict, including my great-uncles in World War I; my grandfather in World War I and World War II; as you know, my dad's service; and my sons—both my sons have been in Iraq or Afghanistan. It's a long history, and I'm very proud of it, and it's obviously had an impact on me and my behavior.