In short, he started yelling, right there in the supermarket. An unnerved bystander summoned a store employee to intervene.

Soon, posts about the altercation had spread on social media, with one former city councilor sharing a Facebook video of herself disguised as a talking toilet-paper roll to bring attention to Scher’s “unhinged behavior.”

By Thursday evening, Scher had prepared a formal apology to Stein, along with the rest of the School Committee. Northampton residents tuned in via Zoom to watch.

“I was the weak link in our local democracy,” Scher, wearing a gray hoodie and standing alone at a podium, said after being introduced by the mayor. “What did I accomplish with this? I didn’t persuade anybody. I couldn’t hear well. I couldn’t listen. I couldn’t find common ground.”

Scher’s apology was directed at a small group of elected officials. But coming as it did amid so much national political strife, it also seemed to speak to a larger sense of keyed-up agitation buzzing beneath everyday life in America.

Discord in national politics has been filtering down to a local level for some time, said Gwen Agna, a former school principal who recently retired from her post as vice chair of the School Committee. “People are very anxious right now, and anxiety can fuel some people not acting in the ways that they might normally.”

Scher is a national political commentator who leans to the left, though not as far left as some in Northampton. He is politics editor of the Washington Monthly, a freelancer for Politico, cohost of the bipartisan online show and podcast “The DMZ,” and author of the book “Wait, Don’t Move To Canada: A Stay-and-Fight Strategy To Win Back America.”

Locally, he’s also known to be a vocal supporter of his wife and her policies, but his defense tactics backfired in Northampton, a city whose slogan is “where the coffee is strong and so are the women.”

“Patriarchal violence — a man rushing to the defense of his woman — has no place in Northampton,“ posted Marianne Milton, who runs the Facebook group Public Comment Northampton. “Cavemen, please find the exit. Women, we can fight our own battles, right?”

Mayor of Northampton Gina-Louise Sciarra (left) walked with Governor Maura Healey and other elected officials during a tour of the downtown district.Erin Clark/Globe Staff

Scher declined to talk further, but as he explained it during his public comment, he had approached Stein the day before when they crossed paths at the supermarket. He had intended to get Stein to “adopt a different tact in his public advocacy,” not to get into an argument, “but when he responded with points I didn’t agree with, I let my emotions get the better of me. I lost my temper, and I raised my voice.”

In a call with the Globe, Stein said Scher kept following him to argue and eventually a store manager had to intervene as two other shoppers witnessed the exchange.

A post about the altercation first appeared on Nextdoor, with the writer identifying herself as a 77-year-old woman from neighboring Westhampton. She was shopping at the Northampton Stop & Shop when she saw two men talking, with one “shouting at the other.”

“I stayed my distance but spoke up and told the shouter that he was frightening me,” she recounted in the post. “The shouter told me that ‘he can do and say what he wants’ — that it was a free country.“

She wrote of Scher: “I was frightened enough to wonder if he was a danger.”

The post racked up comments on Nextdoor and spread on Facebook. Scher soon posted on Nextdoor, saying he apologized to Stein and others in the store “and to my spouse soon after.”

“I don’t want my inappropriate behavior to be a bad example that others emulate,” Scher said at Thursday’s meeting. “If there’s any saving grace to this episode, it is that my shame and regret will be a cautionary tale for others to avoid.”

Members of the Northampton School Committee and the mayor have been fiercely divided in recent months over budget issues and her handling of them. Both local officeholders and residents have expressed concerns about divisive rhetoric and ethical conduct. The mayor has been called a fascist, and, according to Stein, “all the establishment folks have been saying that those pushing for more school funding are ‘Trumpian’ — that they’re being too loud, too aggressive.”

The problem comes down to the fact that despite revenue growth and robust reserves, the schools continue to face staff cuts, said Stein. But the mayor’s office said she can only increase revenues by 2.5 percent each year, while costs rise at a much higher rate than that.

“The schools have not had the money that we’ve needed to fully fund what we think the students need,” said Agna.

The argument is over where to find the recurring revenue to pay for the school’s operating costs at a critical time for Northampton Public Schools.

“It’s a fundamental dispute where the folks who are really getting harmed are the poor kids and the disabled kids and the Black and brown kids,” said Stein. “That’s the fault line.”

Agna said emotions were already running high regarding the city budget. Then, on Wednesday, the whole country was put on edge after a federal immigration officer shot and killed Renee Nicole Good, a 37-year-old mother of three, in Minneapolis.

Former city councilor Quaverly H. Rothenberg, who last month filed a federal lawsuit against Northampton and three other councilors after she was censured for her conduct on a call she made to dispatch services, referenced the shooting as “a Kent State moment” in her public comment Thursday evening.

“The same day that our country’s executive and their gross abuse of power was on full display,” she said, “our executive’s husband was abusing a dissenter.”

At the meeting, one public commenter quoted New York Mayor Zohran Mamdani, who in his inauguration speech spoke about how “those fluent in the good grammar of civility have deployed decorum to mask agendas of cruelty.”

Others called for the mayor herself to formally apologize.

“It just reflects that, somehow, women are responsible for the men that they’re with,” said Agna. “That’s something that feels very old-school to me, very antifeminist.”

In a statement to the Globe Friday, Sciarra said she was “sorry that this happened.”

She added that she has apologized to Stein personally, “and I appreciate the public apology that my husband gave.”

Stein said he also reached out to the mayor and appreciated hearing back from her.

“I think it’s important to lower the temperature,” he said.

Brooke Hauser can be reached at brooke.hauser@globe.com. Follow her @brookehauser.