(RNS) — Jewish leaders and organizations are condemning the appearance of a Nazi flag at a rally for presidential candidate Sen. Bernie Sanders, saying the incident was a clear attack on the politician’s Jewish heritage and raises concerns that anti-Semitic incidents could spike this election season as they did around the 2016 campaign cycle.

Shortly after Sanders took the stage for a rally in Phoenix, Arizona, on Thursday (March 5), the cheering crowd descended into boos when a man in the stands unfurled a Nazi flag. The man then reportedly performed a Nazi salute and shouted anti-Jewish slurs before being escorted off the premises by security forces.

The Anti-Defamation League later identified the man as a known white supremacist and a self-described “stunt activist” who “has harassed a range of Jewish and Muslim organizations and events.”

https://twitter.com/SiddakAhuja/status/1235783420984340482

Sanders responded to the incident while speaking to reporters on Friday.

“I speak not only as a Jewish American, I think I can speak for the families of some 400,000 American troops who died fighting Nazism, fighting fascism, that it is horrific — it is beyond disgusting — to see that, in the United States of America, there are people who would show the emblem of Hitler and Nazism,” he said.

Several major Jewish organizations and leaders also expressed outrage over the incident, noting that it comes in the wake of various recent acts of hate perpetrated against American Jews — including the 2018 mass shooting at the Tree of Life Synagogue in Pittsburgh, Pennsylvania, that left 11 dead.

“Targeting a Jewish candidate with a Nazi flag represents a new level of depravity,” tweeted Jonathan Greenblatt, CEO of the Anti-Defamation League. “There is no place for hate in politics. Disagree on issues, but all good people should flat out reject this kind of poison when it appears in the 2020 race.”

The Religious Action Center of Reform Judaism called the presence of the flag “abhorrent,” tweeting a statement that read: “Antisemitism is unacceptable in any context, and it should have no place in the 2020 campaign. Bigoted attacks on any candidate must be universally condemned.”

Jewish Voice for Peace, an activist organization, noted the appearance of the Nazi flag was especially offensive given that Sanders is “a Jewish man whose family was murdered in the Holocaust” and blamed spikes of anti-Semitism that have tracked with the rise and election of President Donald Trump.

RELATED: Anti-Semitism tops American Jewish concerns in latest survey

“This is the hate Trump has emboldened in the US — and a stark reminder of the time we live in,” read the tweet. “Shout down antisemitism & racism always #safetythroughsolidarity.”

Sophie Ellman-Golan, a liberal organizer who tracks anti-Semitism and works with activist groups such as Never Again Action, said the man’s behavior was particularly galling for its explicit use of Nazi imagery. She said many modern white nationalists such as Richard Spencer tend to use different imagery.

“It’s this sort of surreal, almost old-fashioned anti-Semitism that is reappearing,” she said about the Swastika-bearing flag. “We’ve come full-circle.”

She said that the flag incident challenged misconceptions about the Jewish heritage of Sanders. The Vermont senator has been more vocal about his Jewish roots in recent weeks, publishing videos appealing to Jewish voters and declaring, “I’m very proud to be Jewish and I look forward to becoming the first Jewish president in the history of this country.”

“There has been the denial of Bernie Sanders’ Jewish-ness — but he is Jewish,” Ellman-Golan said. “They’re not doing this just to him; they’re doing it to Jews everywhere.”

Some Jewish figures blamed Trump and the Republican Party for emboldening the kind of anti-Semitism seen at the rally. Rep. Andy Levin, a Michigan Democrat who is Jewish, declared on Twitter that the president and the RNC “cultivated and emboldened” anti-Semitism, which he said “is showing up at a Jewish candidate’s rally, just as it’s shown up in Charlottesville and so many other places.”

Both Trump and various Republican party leaders have condemned anti-Semitism, although critics have argued that the president has been slow to do so.

Ellman-Golan shared Levin’s unease, pointing to anti-Semitic incidents that occurred in and around Trump’s 2016 campaign for president.

“I’m concerned,” she said. “I think it’s only going to increase.”

Even so, she argued that liberal activists are better prepared to stand against anti-Jewish hatred this go-around.

“We know it’s almost entirely coming from the right, and we know that the only way we can defeat it is by building a progressive movement that is strong enough,” she said.

Former Vice President Joe Biden, Sanders’ opponent for the Democratic nomination, also voiced his support on Friday.

“I don’t care who you’re supporting, attacks like this against a man who could be the first Jewish President are disgusting and beyond the pale,” he tweeted.