(CNN)It would be easy for John McCain to be bitter.
After all, he lost two campaigns for president. He spent almost six years in a North Vietnamese prison camp. He has battled the long-lasting injuries from that imprisonment for the rest of his life. He's had melanoma. He's come under attack from his own party for being the deciding vote to end the possibility of repealing and replacing the Affordable Care Act. And, now, he is battling the same form of brain cancer that claimed the lives of Ted Kennedy and Beau Biden.
But, McCain isn't bitter. Instead, he's positively joyful.
"You have got to have joy," the Arizona Republican senator told CNN's Jake Tapper in an interview on "State of the Union" Sunday.
The conversation, which if you haven't watched you really, really should, was largely about policy. Tapper took time at the start of the interview, however, to ask McCain about his health and his life. And, McCain repeatedly acknowledged that while the challenges facing him are real and difficult, he's bringing happiness and joy to the fight.
"I'm facing a challenge," McCain told Tapper at one point. "But I've faced other challenges. And I'm very confident about getting through this one as well." He added later: "There's two ways of looking at these things. And one of them is to celebrate. I am able to celebrate a wonderful life and I will be grateful for additional time that I have."
This is not to paint McCain as a saint. He, by his own admission, isn't one.
McCain has throughout his political career -- which began when he was elected to the House in the early 1980s -- made mistakes, at time major ones. As I wrote last month, the story of McCain's political life isn't unblemished success. It's resilience -- the willingness to get knocked down seven times and get up eight.
That resilience and McCain's "happy warrior" persona is what fueled his rise from an asterisk to a genuine threat to George W. Bush in the 2000 Republican primary fight. It's what he seemed to lose in the wake of that loss as he walked the political wilderness. And it's what he, eventually, found in the low moments of the 2008 campaign when he went from frontrunner to flop and back again.
McCain's joy in the face of a diagnosis that would terrify almost anyone may not make a damn bit of difference legislatively. He has pledged to spend whatever time he has left pushing on the issues -- national security, foreign policy -- he has always cared most deeply about. Given the gridlock that envelops official Washington at the moment, the power of one senator is limited. Still, there is power; McCain's vote with Democrats and a few Republicans effectively killed his party's Obamacare repeal plan.
In a political world in which it seems like the worst behavior is rewarded the most and which people appear to have lost total faith in the men and women they have sent to Washington to represent them, McCain's joy should matter.
It should be a reminder that most politicians are in politics for the right reasons. That politicians can represent the best of us rather than our worst impulses. That getting knocked down isn't a death sentence. That we are a resilient people and that our politics can once again be not only resilient but downright joyful.
Like I said: Go watch the McCain-Tapper interview. You'll be glad you did.