The constituents filing into the Mesa Convention Center one evening in mid-April for the Republican senator Jeff Flake’s town hall had a decidedly un-Republican look. Tattoos and political T-shirts abounded. Activists stood near the entrance distributing stickers, flyers, and other paraphernalia of the resistance and urging attendees to get loud. While chants of “No stupid wall!” and “Health care for all!” echoed through the auditorium, a young woman in a chicken costume wandered the perimeter, clucking and posing for selfies in an act of protest whose meaning remained mysterious to me even after I asked her about it (“Jeff Flake is George Dubya’s chicken,” she said).

Flake couldn’t see any of this from backstage, but he knew that a hostile crowd likely awaited him. The early months of the Trump presidency had inflamed the grassroots left, and Republican lawmakers across the country had lately found themselves standing awkwardly in rooms like this one while liberal voters berated them. Flake is up for reelection next year, and some of his campaign advisers—wanting to avoid the kind of contentious scene that might end up in an attack ad—had suggested that he skip public forums for a while, as many of his colleagues were doing. But he insisted on going ahead.

“People here have legitimate concerns and are afraid,” Flake told me as he waited in the wings. Still, he hoped the audience would be able to distinguish him from the president, whom he spent last year’s election season steadfastly refusing to endorse—making him one of the few Never Trump Republicans in Congress who never caved.

But when it came time for Flake to take the stage, he was met with a fierce swell of hisses and boos. “Thank you!” he said over and over again, without irony. “Thank you!” When the crowd quieted, he took a stab at self-deprecation. “Senators are great at filibustering, but I don’t want to do that. I want to get right to questions.” With that, the flogging began.

The audience battered the senator with one hostile question after another, then interrupted each of his answers. When Flake tried to defend Republicans’ decision to block Merrick Garland’s Supreme Court confirmation, a man near the front barked “Bullshit!” while the rest of the crowd chanted “Shame on you!” When a constituent mentioned the shooting death of an 8-year-old boy in a question about gun laws, Flake began, “As a father, I can’t imagine—” and was promptly met with impatient shouts of “Answer the question!” At one point, a man with a buzz cut walked up and flipped him off with both hands before casually ambling back to his seat.

Throughout the ordeal, Flake remained almost suspiciously good-natured. He waited patiently for each noisy round of jeering to pass, then smiled and invited the next question. After a while, his preternatural niceness began to irritate some people. “I hope behind that smile that you’re doing some serious soul-searching,” one man reprimanded.

As the night wore on, even some of Flake’s detractors expressed grudging respect for his stamina. By the time the town hall wrapped up, he had been going for two and a half hours—blowing well past the scheduled end time. But he noticed a small group of constituents congregated in front of the stage, so he stuck around to chat.

These lingerers were not all, or even mostly, fans, but as Flake talked with them, the vitriol that had permeated the evening seemed to dissipate. Several people thanked him for staying; a couple of them requested his office’s help navigating a tricky bureaucratic issue. One constituent—a friendly guy who would later reveal himself to me as an MSNBC connoisseur—leaned in to deliver Flake a parting message. “Even if you disagree with us on legislation and everything, when the president says these insane things, if … [you] can just stand up and go, ‘We don’t all believe that’—that’s all we’re asking. Just stand up.”

Flake nodded affably. “I appreciate that,” he said, smiling. “I’ve tried to do so.”

Not quite satisfied, the constituent took another run at him. “You’ve got to be a little more …” he began, but adjectives failed him. As the senator moved on to the next handshake, the man’s words hung in the air: A little more what? Brash? Loud? A little more like Donald Trump? Is there no longer a place in politics for someone like Jeff Flake?

With his gently sloped mouth and perpetually arched eyebrows, Flake wears a default expression that might be described as resting troubled and saddened face. He doesn’t relish criticizing other people, but when he does, it is usually in a fatherly tone of disappointment (he has five children, who have presumably given him some practice). He sometimes seems as if he has just crash-landed here in a time machine from some bygone era of seersucker suits and polite disagreements. In today’s climate of staged presidential beheadings, and reporter body-slamming, and senatorial f-bomb-dropping, the gentleman from Arizona seems altogether uncomfortable. “I’m not a fan of the way it’s become,” he told me when I visited his Capitol Hill office a few weeks after the struggle session in Mesa.

Complaints like this are endemic in Washington, of course. Whichever party’s base is more fired up at any given moment, you can bet the leaders on the other side have recently rediscovered a reverence for decorum. But Flake’s indictment of this political moment is unusual because it implicates his own party. After a decade and a half in Congress, he has come to believe that the defining story of his time in Washington is one of goodwill gutted and cynicism weaponized, culminating with the election of Donald Trump.

When I asked him to pinpoint the beginning of this story, he recalled the fallout from the 2000 presidential election (“A lot of Democrats just didn’t want to recognize Bush as a legitimate president”), as well as rabid right-wing attacks on Barack Obama. (Flake was among a small handful of Republicans who formally admonished their colleague Joe Wilson for shouting “You lie!” at Obama during a presidential address to Congress.) “I frankly enjoy watching the House of Commons,” he told me, offering up his best imitation of a feisty MP—“Ah, rubbish!”—before returning to his point. “But this is a different system,” he said. “I think you have to have some kind of decorum here.”

For Flake, one of the most jarring illustrations of Washington’s growing decency deficit came the night of the 2012 State of the Union address. He was seated next to Gabby Giffords, a friend and fellow member of Arizona’s congressional delegation. Giffords, a Democrat, had been shot in the head a year before and was still struggling to recover. Throughout the evening, Flake gently helped her up when she wanted to join the Democrats in a standing ovation—a gesture that meant he was often the only Republican on his feet during Obama’s applause lines. “I started getting texts and emails from people saying, ‘Why are you standing? Why are you standing?’

Things only proceeded to get worse. Flake watched Trump’s various instigations on the campaign trail with growing alarm. “I mean, you watch those rallies, Republican rallies, the ‘Lock her up!’ chants, the depictions of Hillary Clinton, the posters that are just—” He sighed. “It’s beyond the pale.”

Plenty of Republicans criticized Flake for his refusal to fall in line behind Trump. But perhaps his gravest sin against the gods of partisanship was a tweet he sent after Clinton tapped Senator Tim Kaine as her running mate: “Trying to count the ways I hate @timkaine. Drawing a blank. Congrats to a good man and a good friend.” Many Capitol Hill Republicans were apoplectic, Flake told me, recounting a surreal meeting in which one stood up and said, “If you can’t say anything mean, then don’t say anything at all!” The admonition, made with no discernible self-awareness, struck Flake as “a stark admission that we have really gone off the rails.”

As we spoke, Flake repeatedly stressed that he was not fretting over the coarsened political culture simply because he finds it distasteful, nor was he advocating bipartisanship for its own sake. A libertarian-minded Republican with a pristinely conservative voting record, he insists that he has not gone “squishy,” and that he harbors no desire to “sing ‘Kumbaya.’ ” But the decline of civility in politics, he said, has made it nearly impossible for government to function properly.

He seems to blame this state of affairs primarily on the political leaders who cynically egg on their base’s bad behavior. At one point during our conversation, while Flake described the “unbelievable” language he had seen deployed on social media, I asked whether Trump’s Twitter feed colored his assessment.

The senator’s eyes flashed with what seemed like real outrage. “Yeah!” he exclaimed. “Yeah! You always expect that there are going to be people out there who do it, but for politicians to join in, lead the charge, not condemn it—that’s what’s troubling.”

In Flake’s view, Trump is both a product of the rot afflicting politics and a cause of its continued decay. “It didn’t start with him, but he’s taken advantage of it.” He pointed to the “birther” episode—in which Trump became an overnight sensation on the right by suggesting Obama was a secret foreigner—as emblematic of his party’s failures. “It was just wrong,” he said. “People who knew better should have stood up.”

Flake was raised on a cattle ranch in Arizona, in a giant Mormon family—an upbringing that he says influenced both his political style and his outlook, particularly on immigration. “I grew up alongside migrant labor,” he told me, rattling off the names of Latino workers his family had befriended. “I could never look at them and see a criminal class.” In 2013, Flake was part of the bipartisan “Gang of Eight,” which helped pass a comprehensive immigration-reform bill in the Senate (it died in the House). He recalled for me his deep personal frustration watching Trump and his fellow Republicans make naked appeals to “nativist sentiment” last year. When Kaine traveled to Florida and in fluent Spanish praised the patriotism of newly naturalized citizens, “I almost cried,” Flake said. “I just thought, That should be us. That was us, and now it’s not.”

Talk like this will do little to win over the GOP’s Trumpian wing, of course. Already, Flake has one primary challenger—an immigration hawk who attacked him on Breitbart.com as a “big-government globalist”—and Trump has reportedly threatened to spend $10 million to take him down.

Apparently undeterred, Flake spent much of this year finishing a book in which he sharply contrasts Trump’s brand of conservatism with his own vision. Flake told me he wrote the book largely in secret because he knew his campaign consultants would try to talk him out of publishing it during his primary race. “You can always find an excuse to not stand up for your principles,” he said. “But if you don’t risk anything, it doesn’t matter as much.”

All of which raises a larger question about where Flake fits at this fraught moment. He clearly sees himself as engaged in a fight for the soul of his party—beating back the barbarian populists at the gate, standing up for decency and old-fashioned conservative values. But the political battlefield has never looked more uninviting to a warrior of Flake’s kind.

On the morning of June 14, a 66-year-old man armed with a rifle opened fire on a park in Alexandria, Virginia, where Flake was practicing with his fellow GOP legislators for the upcoming Congressional Baseball Game. For several harrowing minutes, police tried to subdue the shooter, and lawmakers scrambled for cover. By the time it was over, five people had been shot. Flake rushed to the side of the Louisiana congressman Steve Scalise, who lay soaked in blood, and helped apply pressure to his wound as they waited for medics to arrive. He then called Scalise’s wife, so that she wouldn’t find out about the shooting on TV.

In another era, an event like this might have occasioned a brief respite from partisan acrimony. But any hope of that was lost as soon as it was reported that the shooter was a former campaign volunteer for Bernie Sanders and an eager participant in the online cesspool that now passes for political discourse. “Trump is a traitor,” he had written on Facebook. “Trump Has Destroyed Our Democracy. It’s Time to Destroy Trump & Co.” Conservatives pounced, accusing Democrats of stoking hysteria and violence. The left responded with its own recriminations, and some smirking about the GOP’s gun-control platform.

Flake, for his part, barely had time to change out of his blood-spattered clothes before his conservative primary opponent’s campaign sent out an email denouncing his “America Last” policies and pledging that his “days in the Senate are numbered.” Flake’s aides spent the day monitoring the comments on his official Facebook page for hate speech and threats. “I hope the next guy has better aim,” read one deleted comment.

When I visited Flake and his wife, Cheryl, in his office on Capitol Hill the day after the shooting, he looked drained. Resting his head on the back of his armchair, he recounted the preceding 24 hours in a quiet, halting voice. “It was a long day,” he said, glancing at Cheryl. “Just—I’m just glad to be here.” He seemed to view the episode as a grim validation of his worst fears about the country. “The deterioration of political discourse in general aids this,” he said. “When we ascribe motives to our opponents, that they are evil, then we’ve almost given license to extreme behavior.”

Cheryl marveled at how the climate had worsened since her husband first took office. “Up until, I’d say, this past year, I’ve never felt threatened or unsafe.” But as the political onslaught against Flake has intensified—from both sides—so too has her fear of their family getting caught in the crossfire. She no longer allows photos of their children to appear on campaign billboards or Flake’s public social-media accounts. Unruly public forums now make her skittish, and she has begun to worry about their home’s security. Earlier this year, a group of protesters staged a rowdy demonstration just outside their Mesa subdivision. “I’d never felt so grateful that I lived in a gated community,” she said. “And that’s not who I am.”

About a mile from where we sat, thousands of people were streaming into Nationals Park to take in the Congressional Baseball Game that evening. Ticket sales had spiked in the day since the shooting, and people on TV were asking whether this moment of patriotic unity might serve as a healing balm for a nation sick with rage. Flake wanted to believe that, but he remembered better than most the last time an attack on a lawmaker was supposed to usher in a new era of civility.

“This tends not to last,” he said. Still, he insisted he wasn’t giving up hope. “I don’t know how much further you can go this way before people recoil and say, ‘Let’s change it.’ ”

This article has been updated from the print version of the September issue.