As recently as last week, with less than a month to go before the general election in the U.K., the position of the country’s Conservative Party looked secure. The Prime Minister, Theresa May, had been projecting a protective national steadfastness through the process of Brexit, and with the momentum behind the right-wing U.K. Independence Party dissipating and the Labour Party convulsed by internal grievances and recriminations, the Tories looked likely to win a historic victory.

But then the Conservatives made a mistake. Last Thursday, the Party published an election “manifesto”: a sketch of a policy program whose proposed changes to the public health system contained a very alarming detail. Under the Party’s plan, certain patients whose disease or disability required the public health-insurance system to supply in-home care could have their house possessed by the state after they died, as a way for the government to recoup the costs of their care. The “dementia tax,” as it was almost immediately dubbed, carried the brutal suggestion that a Party whose majorities had been built by the votes of older people in smaller towns was arranging for the state to take these constituents’ homes once they died. The lampoonable Labour leader, Jeremy Corbyn, saw a sudden spike in his popularity numbers. The polls went into chaos. May accused Labour and the media of making alarmist claims, and argued weakly about the basic compromises necessary to insure care for an aging population. “Nothing has changed, nothing has changed,” May muttered, to Parliament. Maybe not, but the march to a conservative majority, which had seemed so assured, had developed a nervous, patrician cough.

During the past year, the language of populism has given center-right politicians on both sides of the Atlantic access to a bristling and hostile energy, a mood of existential impatience. But now the same politicians are struggling to resolve the contradictions of the movement that brought them to power. On Wednesday, at a little after four o’clock, the Congressional Budget Office released its assessment of the latest Republican health-care-reform proposal, the American Health Care Act, which the House passed earlier this month. Among other alarming findings, the C.B.O. said that the bill, if adopted by the Senate and signed by the President, would cause twenty-three million Americans to lose their health insurance over the next decade.

In the halls of the Capitol, reporters found Mark Meadows, the doctrinaire conservative and Freedom Caucus leader, whose support for the A.H.C.A. was instrumental to its success in the House. Meadows said that he was relatively sanguine about the score, but added that he had not yet had a chance to read the C.B.O. report in full.* A reporter asked him about one passage in particular. Though Republicans had long promised that their plan would protect patients with preëxisting conditions, the C.B.O. had found that those patients “would ultimately be unable to purchase comprehensive . . . insurance at premiums comparable to those under current law, if they could purchase it at all.” Meadows read this section of the C.B.O.’s assessment on a reporter’s phone, and then he started to tear up. “Listen, I lost my sister to breast cancer,” he said. “I lost my dad to lung cancer. If anybody is sensitive to preëxisting conditions, it’s me. I’m not going to make a political decision today that affects somebody’s sister or father, because I wouldn’t do it to myself.”

Republican political operatives had been anxious about the C.B.O. report, since the timing of its release coincided with a special election in Montana, where voters are choosing on Thursday between a Democrat and a Republican to take the seat previously held by Ryan Zinke, who is now President Trump’s Interior Secretary. The Democrat in the race, Rob Quist, had built his candidacy largely around attacking the Republican health-care plan, and his Republican opponent, Greg Gianforte, had declined to say whether he supported the bill, saying he was waiting for the C.B.O. score.

On Wednesday evening, the day before the polls were to close, Gianforte was setting up for an interview with a Fox News crew when he was approached by Ben Jacobs, a political reporter for the Guardian, who said that he wanted to ask Gianforte about his position on the health-care bill, now that the C.B.O. score had been made public. “We’ll talk to you about that later,” Gianforte said. Jacobs pressed him—there wouldn’t be time later, as Election Day was just hours away. “I’m sick and tired of you guys!” the politician yelled. And then Gianforte, a fifty-six-year-old millionaire congressional candidate, attacked Jacobs.

The attack did not last long. Eyewitness accounts have differed mostly in which part of the attack they emphasized. Jacobs himself said that Gianforte “body slammed me.” The Fox News reporters who watched it happen said that the politician also grabbed the reporter’s neck, and punched him once he was on the ground. The Guardian has posted audio of the attack, in which Gianforte can be heard screaming “Get the hell out of here.” (The Gianforte campaign would later release a statement suggesting that Jacobs had asked “badgering questions” and “declined” to lower his recorder after the politician asked him to do so.) The reporter ended up in the hospital, where doctors took X-rays. The politician wound up being interviewed by sheriff’s deputies, who by the end of the evening had charged him with misdemeanor assault. As Montanans went to the polls Thursday morning, the image on the front page of newspapers was of Gianforte after the attack, sitting in the seat of an S.U.V., looking glum.

That was Wednesday night’s news, and Thursday morning’s. Maybe Gianforte is just a brute. But his actions follow a deeper current. The nationalist surge of 2016 was premised on an unusual promise, made by parties on the right: that conservatives would be the true protectors of the social safety net, rather than the progressives who had designed the system. The campaigners for Brexit promised that three hundred and fifty million pounds a week, which had previously been sent to Europe, could instead be used to strengthen the National Health Service. It was a ludicrous claim, but not much more so than Donald Trump’s promises to replace Obamacare with “something terrific,” an unspecified program under which better health care would come at “a fraction of the price,” and which would protect Medicaid funds as well as people with preëxisting conditions. Conservatives implied that they had changed, that they were no longer devoted to a libertarian gutting of social welfare but a nationalistic protection of it. The politics at work here were obvious: blame immigrants and out-groups for siphoning money from the working classes, and promise that, by excluding those groups, there would finally be more to go around.

In scenes around the world this month—in London, in the hallway near Meadows’s office, and in Gianforte’s Bozeman, Montana, campaign headquarters—this promise is coming under the pressure of its own impossibility. To build a stronger social-welfare system generally requires more money, and conservatives remain devoted to giving it less. The early successes of the resistance—the town halls and the marches—have come when the left has been able to demonstrate and speak out about how much ordinary people stand to lose. But the situation has also concentrated pressure on individual elected officials who stand before crowds, trying to explain how promises to defend social welfare have dissolved into a more predictable conservatism.

“Get the hell out of here,” Gianforte said, after Jacobs had promised to call the cops about the assault. The candidate’s voice was softening by then, the sound of a man who has relieved an immediate source of stress and has not yet realized the scale of the stress to come.

*This post has been updated to better reflect that Congressman Mark Meadows was asked about the C.B.O. score shortly after it came out.