Wursthall Restaurant & Bierhaus in San Mateo, Calif, where there wasn't really a ban against MAGA hats. (Michael Macor/San Francisco Chronicle via AP, File)

The tweet, sent out on a Sunday, did not make a big splash at the time.

It was the end of another draining week of political news in the United States, this time dominated by a debate about the actions of some teenagers wearing Make America Great Again hats. J. Kenji López-Alt, a chef, writer and part owner of a beer hall in California, took to Twitter to say he felt the hats were an expression of intolerance.

“It hasn’t happened yet, but if you come to my restaurant wearing a MAGA cap, you aren’t getting served, same as if you come in wearing a swastika, white hood, or any other symbol of intolerance and hate,” he wrote.

By Wednesday, the remark had been retweeted a relatively modest 200 times, hardly a viral news story or prompt for a national debate.

But after the San Francisco Chronicle wrote a story that described López-Alt’s statement as a MAGA-hat ban at his restaurant, Wursthall, the story began to spread. It was covered by other news outlets, both locally and beyond, such as the Hill and the Associated Press.

Right-wing sites such as the Daily Caller, Breitbart, the Daily Wire and Fox News picked it up too, reporting it as another anecdote in the long-standing grievance about how conservatives are supposedly the victims of liberal intolerance. It didn’t hurt that the restaurant was in San Mateo, a city of about 100,000 south of San Francisco that is considered part of largely liberal Silicon Valley. Russian state media outlet RT also piled on.

But there was a problem with the framing of the coverage: It wasn’t really true. There was no MAGA-hat ban at the restaurant; there never was, López-Alt says. It does not appear that anyone was prevented from eating at the restaurant. (Some outlets did more accurately frame the issue around the chef’s remarks.)

A news cycle had been touched off because a chef’s angry tweet had played into a narrative — that conservatives are under fire by liberals — but without any customers actually being affected.

López-Alt deleted the tweet by Thursday as it drew media attention.

Still, the story continued to travel.

In a brief phone interview with The Washington Post, López-Alt said the restaurant had no ban “on any kind of clothing, including MAGA hats.”

“There isn’t one and never has been one,” he said. He declined to comment further.

The story is a case study of how mainstream media outlets can contribute to the contentious national dialogue, sometimes amplifying social media outrage instead of properly contextualizing it.

Whitney Phillips, an assistant professor of communication and rhetorical studies at Syracuse University who wrote a recent report about the pitfalls of the digital news cycle, said that stories like ones about López-Alt were a reminder that media manipulation is not just about shadowy troll armies in other countries.

Media distortion is the result of a complex mix of factors, she said: a relentless right-wing mediasphere that influences the direction of centrist and left-leaning media, even when it is silent; mainstream news outlets' efforts to mine social media for emotional yarns to draw readers; and opaque algorithms that surface digital content in a way which makes the origin of stories hard to pin down.

“We have a very difficult time distinguishing an authentic story from something that’s manufactured,” Phillips said. “It’s not like there’s some kind of grand conspiracy — people getting together and constructing narratives. It’s all of these forces crashing together, and as a result you get a garbage fire all the time.”

Stories like the one about Wursthall become less about what happened than what they symbolize — imbuing them with a political undertone.

“The specifics of the story fall by the wayside, and the symbolism is very easy to manipulate to your personal ends,” Phillips said.

The story about the Covington Catholic High School boys is perhaps a good example of this. The details of the encounter between a Native American activist and a MAGA-hat wearing high school student, amplified with edited video on social media, spurred news coverage that was later called into question after additional videos emerged. The incident is now seemingly in perpetual dispute. And the identities behind two of the Twitter accounts that helped the video draw attention remain unknown. But the reality of the political debate it kicked off now exists as an undisputed truth.

The debate about MAGA hats has peaked in recent weeks. Many, such as Washington Post fashion critic Robin Givhan, have argued that the hat is an expression of racial insensitivity and hate, akin to the Confederate flag. Commentators on the right say that the anger about the hats is an indication of the intolerance of the left.

López-Alt posted an apology on the site Medium on Friday morning, speaking of his mixed-race heritage — his mother is from Japan — and saying that he had come to believe that MAGA hats were symbol of “anger, hate and violence.” But he admitted that the way he had expressed his feelings had “ended up only amplifying the anger,” making some feel as if a message of hate was directed at them.

“My message was intended to reject anger, hate and violence, and indicate that these shouldn’t be welcomed in our society and aren’t welcome in our community. It was meant to be directed at those who would try to bring messages of hate, violence, and anger into my place of business, no matter what form it comes in,” he said.

His Twitter account has been inundated by angry responses from the pro-Trump crowd on Twitter, some of whom threatened to boycott the business and López-Alt’s cookbooks. Yelp disabled review writing on the restaurant’s page, something it does for fake reviews by angry commenters. San Mateo Police Department spokesman Michael Haobsh said the agency was monitoring the situation but had no reports of specific threats.

López-Alt said the restaurant’s policy would continue as it had been: “to serve all customer regardless of race, color, religion, sex, national origin, sexual preference, gender orientation, disability, or political opinion — so long as they leave hate, anger, and violence outside of the doors.”

Abby Ohlheiser contributed to this report.

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