Eighty years ago Wednesday, a group of American Nazi sympathizers rallied in New York City. In light of that, we’re republishing The Post’s October 2017 story about a man who tried to disrupt that rally — an event central to the Oscar-nominated film “A Night at the Garden.”

Shortly after the Loma Prieta earthquake struck the San Francisco Bay area in 1989, the Los Angeles Times spoke with local residents about the likelihood that they, too, would experience a significant quake at some point in the near future.

One man the newspaper spoke with was stoic about the prospect.

“When it comes, it comes. Not much use worrying about it,” local fisherman Isadore Greenbaum told the paper. “I remember when one hit a ways back, some of the people didn’t know what it was, and I told ’em it was just a whale scratching its back.”

What the Times doesn’t seem to have known is that they were speaking with someone with a proven track record of bravery in the face of danger. Isadore Greenbaum was arrested in 1939 for charging the stage at a rally of 22,000 Nazi sympathizers in the middle of Manhattan, enduring a beating at the hands of the uniformed stormtroopers who were providing security before being dragged away by the police.

That rally is the subject of a recently released short film, “A Night at the Garden,” showing scenes from inside Madison Square Garden during the event. The footage is chilling, showing the pomp and ceremony we’re used to seeing from Nazi Germany being re-created in the United States.

Organized by a group called the German American Bund, the rally featured a speech by Fritz Kuhn, who was naturalized as an American citizen five years earlier. According to the book “Swastika Nation,” which documents the Bund and the 1939 rally, Kuhn at one time worked for Henry Ford, who himself was notoriously anti-Semitic. Kuhn was referred to as the Bundesführer, and at the beginning of his speech in New York, he made reference to his reputation.

“You all have heard of me,” he said to laughter. “To the Jewish-controlled press: as a creature with horns, a cloven hoof, and a long tail.” Kuhn spoke in front of an immense portrait of George Washington, whose birthday the event was meant to mark. Washington, in the estimation of the Bund, was the first fascist leader.

Isadore Greenbaum, then 26, was in the audience. A plumber’s helper by trade, he lived in Brooklyn (in what is now East Williamsburg) with his wife, Gertrude, and his young son. He’d sneaked into the rally and grew angrier and angrier as he listened to Kuhn speak.

“Oblivious to the [Ordnungsdienst, or OD] guards, he charged toward Kuhn,” Arnie Bernstein writes in “Swastika Nation.” Greenbaum yelled, “Down with Hitler!”

“Podium microphones amplified the sounds of his feet on the stage. The OD swarmed him with everything they had, subduing Greenbaum with effective punches and stomps. It was an uncanny replication of Nazi street thuggery, a pack of uniformed men blasting away with fists and boots on a lone Jewish victim. The audience shouted their approval at this unexpected development, a physical Jew bashing that intensified and underscored everything the Washington’s Birthday celebration really stood for.”

In the footage from the film, you can see the glee of the young men in the band on the stage as Greenbaum is assailed — and Greenbaum’s terror as he’s dragged off the stage by the police, losing his pants to the crowd.

Kuhn kept talking, to raucous applause. In December of that year, he was arrested for embezzlement and convicted by Manhattan District Attorney Thomas E. Dewey, known to history for his loss in the 1948 presidential election but disparaged by Kuhn in that rally as Thomas Jewey.

Greenbaum was arrested immediately and taken to the police station. He faced 10 days in jail unless he paid a $25 fine for disorderly conduct; his wife managed to scrape the money together.

The New York Times described his interaction with the judge who levied that sentence.

“I went down to the Garden without any intention of interrupting,” Greenbaum said, “but being that they talked so much against my religion and there was so much persecution I lost my head and I felt it was my duty to talk.”

“Don’t you realize that innocent people might have been killed?” the judge asked.

“Do you realize that plenty of Jewish people might be killed with their persecution up there?” Greenbaum replied.

Two years later, the United States went to war with Nazi Germany. Greenbaum signed up, first serving as deck engineer and eventually attaining the rank of chief petty officer. He was interviewed by Stars and Stripes in an article headlined “One Punch Izzy Still in There Punching” — apparently given that title because Greenbaum claimed to have laid a fist on Kuhn (which he doesn’t seem to have actually done).

Greenbaum explained to Stars and Stripes’ Victor Lasky (who went on to become a prominent conservative columnist) why he’d done it: “Gee, what would you have done if you were in my place listening to that s.o.b. hollering against the government and publicly kissing [Adolf] Hitler’s behind — while thousands cheered? Well, I did it.”

Bernstein writes that Greenbaum had firsthand experience with Hitler’s Germany, having traveled there in 1933 shortly after Hitler took power. Greenbaum’s journey back seems to have been documented by the U.S. government; a man matching his name and birth date is listed as a stowaway on a voyage of the SS Manhattan from Hamburg back to New York in early 1934.

Eventually, Greenbaum and his wife moved to Southern California, where he spent the rest of his life. He died in 1997.

His fame as a fisherman on the Newport Pier — where he’d “kept up a 30-year tradition of making ‘monuments’ at Newport Pier out of newspaper clippings, Bible verses and American flags,” according to one memorial — led to a brief mention of his passing on the local news.

“Before he passed on to heaven, he asked me to get a hot dog and call the media,” his granddaughter told a reporter. “And that’s what I did. And a Heineken.”

When he spoke with the Los Angeles Times about earthquakes in 1989, he explained what his last thoughts would likely be.

“The whole place starts to shake,” he said, “and I’d be thinking, ‘Why was I so bad to my wife? I love her. I gotta repent.’ ”

“But,” he added, “what can you do about it?”

Greenbaum is buried next to Gertrude, who died in 2010. His tombstone includes a quote from II Corinthians: “Absent from the body, present with the Lord.”