There was a disturbing incident at a Bernie Sanders rally in Phoenix, Arizona on Thursday. A protester interrupted Sanders's speech by unfurling an five-foot-long Nazi banner and screamed "Heil Hitler" with his arm raised in a Nazi salute.

The fact that Bernie Sanders is Jewish made the gesture even more disgusting.

Ron Mack, 40, said that at the beginning of Sanders's speech the man began shouting anti-Semitic slurs at the candidate. "He never put his arm down," Mack said according to Buzzfeed News. "Everybody was in disbelief."

The shocking display didn't go on for long. A few seconds after the banner was hung in the top deck at the 7,000-person Arizona Veterans Memorial Coliseum, security ushered the man and his paraphernalia out of the building.

The Anti-Defamation League (ADL) later identified the anti-Semite as Robert Sterkeson, a white supremacist who has "harassed a range of Jewish and Muslim organizations and events."

Witnesses say that Sanders appeared to have heard the outburst and looked up in the stands, but that was after the banner had been taken down. "The senator is aware of the flag with the swastika on it and is disturbed by it," Sanders' communications director, Mike Casca, said in a statement.

The incident occurred on the same day Sanders posted a video on Twitter celebrating his Jewish heritage.

"As it happens, my father's family was wiped out by Hitler," Sanders says in the video. "If there is any people on earth who understands the danger of racism and white nationalism, it is certainly the Jewish people."

"Anti-Semitism is on the rise because — I'm not saying it wasn't there before, but now the stamp of approval has been given to hatred," Kati Preston, a Holocaust survivor, says in the video.

As evidenced by the Nazi in the stands at the Sanders rally, anti-Semitism has been on the rise in the U.S. since Donald Trump became president.

According to the ADL, there were 1,879 recorded Anti-Semitic incidents in the United States, with a dramatic increase in physical assaults. "Assault, harassment and vandalism against Jews remain at near-historic levels in the U.S.," the ADL writes on its website.

"Assault, harassment and vandalism against Jews remain at near-historic levels in the U.S. The deadly attacks in synagogues in Pittsburgh and Poway have made American Jews feel more vulnerable than they have felt in decades," the ADL continues.

Unfortunately, the incident is a visceral reminder that anti-Semitism is alive and well in America and it has no place in its politics.

It's also a reminder of what is at stake in the 2020 election.

America has the chance to do an about-face and turn against the type of divisive hatred that suggests that some white supremacists are "very fine people" and select a leader, such as Sanders, who unequivocally condemns white supremacy.

"You have a president who doesn't have the guts to say what the vast majority of the people understand to be true, that white supremacy and neo-Nazism have got to be condemned," Sanders said after the Charlottesville rally in 2017 in which an anti-Nazi protestor was killed.