With Republican presidential candidate Donald Trump’s big MAGA rally at Madison Square Garden on Sunday will come memories of the thousands of Nazi supporters who crowded into a New York venue of the same name in 1939.

We should also remember the bravery of 26-year-old Isadore Greenbaum, a Jewish plumber’s helper, hotel worker, cab driver and waiter from Brooklyn who attended the supposed “pro-American” event out curiosity, but found himself unable to just sit and listen to venomous bigotry being passed off as patriotism.

“He just lost it,” his grandson, Brett Siciliano, told the Daily Beast. “My grandfather was not a violent guy, but he didn’t take much s–-t, either.”

The moment when Greenbaum took action in defiance of some 22,000 Nazis can be seen in the 2017 Oscar-nominated documentary short film, A Night at the Garden. Its footage shows Fritz Kuhn, a German immigrant auto worker turned “fuhrer” of U.S. based Nazi organization the German-American Bund. In the footage, he is standing at a podium set before a 30-foot-tall portrait of George Washington flanked by American flag banners decorated with Swastikas.

“We with American ideals, demand that our government shall be returned to the American people who founded it,” Kuhn says, seeking to disguise hatred as “Americanism” while spewing venom against Jews—rhetoric comparable to that Trump has increasingly been directing against migrants.

Kuhn is then interrupted by a commotion.

Greenbaum had listened until he reached a limit. He then made his way to the front through the cheering anti-semites and rushed the stage.

He wanted “to shut the guy up,” his grandson explained. “He grabbed the mic wires, and when that was not working, he kept going to the podium.”

As Greenbaum cried out ”Down with Hitler!” a squad of stormtroopers in Nazi uniforms pounced, they set to punching and stomping him while onlookers cheered.

A half dozen of the 1,700 uniformed New York City cops deployed for the event intervened, simultaneously rescuing and arresting Greenbaum. He had a broken nose and his pants were shredded.

The next day, Der Angriff, the German newspaper controlled by Nazi propaganda minister Joseph Goebbels ran the headline “Jewish Attempt on Fuehrer of German-Americans in New York.” The accompanying article described Greenbaum as “a Jew who tried to assassinate Kuhn after attempts to kill him politically had failed.”

Greenbaum offered his own description of his actions when he was arraigned in West Side Court on a charge of disorderly conduct.

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

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

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

He pleaded guilty to the charge and was given the choice of either paying a $25 fine or serving 10 days in jail. The admirers who took up a collection for the fine included the arresting officers. His wife Gertrude had been sitting in the courtroom with their first child, a 16-month-old son. A news photographer snapped a picture of her kissing her newly released hero husband in the back of a cab as they departed.

“I think the judge kicked in, too,” his grandson told the Daily Beast.

When Hitler invaded Poland six months later, Greenbaum was one American who had already battled Nazis. The whole country went to war against Hitler in 1941 and Greenbaum signed on with U.S. Army Transport, serving as a deckhand and then chief petty officer. He made 15 round trips across the Atlantic and was once torpedoed.

“It’s good to be fighting against the hated Nazis again,” he was quoted saying in a Liverpool Evening Express article. “If we had stopped them earlier when we had the chance there would be a lot less bloodshed in the world today.”

After the war’s end, Greenbaum had two more children. He eventually moved to California, where one of his daughters, Siciliano’s mother, had settled with her husband. He took to fishing from the Newport Beach Pier, where he became known as Pops. (His favorite spot was at the pier’s southeast end, which became known as “Pops’ Corner.”) He set an American flag down every day, sometimes cooking the day’s catch there and then distributing it to the homeless. He often told stories of his early days as an orphan in Hell’s Kitchen and then Williamsburg.

He also often told the story of that night with the Nazis at Madison Square Garden.

“We used to tease him, ‘Not again, grandpa,” Siciliano said .

Siciliano was with Greenbaum when, aged 84, he succumbed to advancing age and declining health in 1997.

“He died in my arms,” Siciliano remembered.

Now, 85 years after Greenbaum’s night at the old Madison Square Garden, Trump will be taking a podium at the new venue with the same name. He is all but sure to cloak hatred as patriotism in a way no true American should tolerate.

“He loves too many dictators,” Siciliano said of Trump.