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What does it mean that Nazis are comfortable waving swastikas at a Sanders rally?

At a rally in Phoenix, Arizona, on Thursday evening, Vermont Sen. Bernie Sanders was greeted with raucous cheers, thunderous applause, and — in a stunning instance of shockingly brazen bigotry — an unapologetic neo-Nazi, who proudly unfurled a Swastika banner behind Sanders's lectern.

The incident was captured on video which quickly went viral. It's the latest in a long line of anti-Semitic attacks on Sanders, arguably the most high-profile Jewish politician in America, who now stands as one of the only two viable Democratic candidates for his party's nomination to be president. Those attacks have come both from those who hate Sanders simply for being Jewish, and those who have paradoxically accused him of being anti-Semitic himself for his progressive stances on issues such as Palestinian rights.

Sanders himself has been increasingly vocal about his heritage, opening up about his having lost family during the Holocaust and tweeting just hours before Thursday's rally that he "would be very proud to be the first Jewish president."

Which makes what happened in Phoenix all the more troubling. "I don't recall another incident over the course of the campaign where we've seen a Nazi flag unfurled at a Sanders event, or any other candidate's event to date," Anti-Defamation League CEO Jonathan Greenblatt tells Mic.

"However," he says, "it is not inconsistent with the alarming pattern of Anti-Semitism being seen online being directed at the candidate."

Greenblatt notes that other candidates — particularly Mike Bloomberg, the former New York City mayor who dropped out of the race this week but is also Jewish — also faced their own anti-Semitic attacks. "It's not unique to Sanders," he says. "But his prominence is concerning for us because we don't want to see this kind of intolerance and malice mainstreamed. And as someone who had most of his extended family killed by the Nazis in World War II, this kind of imagery aimed at Sen. Sanders is particularly insensitive."

Becca Lubow, a Sanders supporter and activist with the progressive Jewish organization IfNotNow, is slightly more pointed in her assessment of what the swastika incident means.

"It was hard to watch that video for me," Lubow tells Mic, "because the rising anti-Semitism and white nationalism in this country right now is terrifying, and is unlike anything I've experienced for most of my life."

"I don't see [Trump] as an ideological anti-Semite, but he certainly has degraded political discourse in America."

Indeed, while an undercurrent of anti-Semitism has been a factor of American life for generations now, the past few years have seen a noticeable uptick in public displays of overt hatred of Jews — one that, while not necessarily directly caused by the ascendency of Donald Trump, certainly corresponds with his rise in political life.

"I don't think it would make sense to see Trump and Trump alone as the fountainhead for an uprise in anti-Semitism," explains Professor Alvin Rosenfeld, director of the Institute for the Study of Contemporary Antisemitism at Indiana University. "But, there are groups — they showed up of course in Charlottesville, Virginia, before that they showed up, only a few weeks after he was voted in, at the rally in Washington, D.C. — feeling license to raise their arms in Nazi-like salutes."

"I don't see [Trump] as an ideological anti-Semite, but he certainly has degraded political discourse in America," Rosenfeld continues. "And that's allowed a whole range of people to feel at license to say things that they would have thought twice and three times in the past from saying publicly."

For Lubow, however, Thursday's incident can be traced directly back to Trump, whose rhetoric she links to the 2018 massacre of Jewish worshippers at the Tree of Life synagogue in Pittsburgh.

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"I am very, very frightened of the impact that he's having on our country — not just for Jews. He's also making our neighbors unsafe. He's making Muslims unsafe, he's making immigrants unsafe," Lubow says. "Trump tries to say that because he supports Israel's right-wing government, he's a friend of the Jews. And we know that's a lie, because we can see what he's doing to embolden anti-Semitism and white nationalism here."

For Stosh Colter, CEO of Bend the Arc, another progressive Jewish organization, what happened in Phoenix is part of not only a national trend toward hate, but a global one as well.

"This was not an isolated incident — it’s a reflection of how white nationalists are growing in confidence as they have been embraced and emboldened by political leaders in Congress and the White House," Colter said in a press release provided to Mic. "It's the same white nationalism that inspires mass shootings in Pittsburgh, Poway, El Paso, Charleston, Christchurch, and more. It's the same white nationalism that animates xenophobic policies like immigrant detention camps and the Muslim ban, and tells progressive women of color to 'go back' to where they 'belong.""

"Bernie represents the best of this Jewish call to pursue justice."

Both Rosenfeld and Greenblatt say there is a solution to this emboldened anti-Semitism: immediate and unequivocal condemnation from communal leaders.

"It starts with leaders leading, and calling out hate whenever it happens — on both sides of the spectrum," Greenblatt says. "Particularly on your own side, when your own partisans engage in prejudice, responsible people in public life need to call it out immediately."

Meanwhile, Lubow and Rosenfeld offer a dire prediction for the future: As Sanders continues to maintain a high public profile, so too will we likely see more examples of these types of overt anti-Semitic incidents.

"Bernie, because he's so visibly Jewish, is potentially going to engender more of that response," Lubow says. "I also believe that even though Jewish visibility can be frightening, it's important to confront this rising anti-semitism and white nationalism head on. Bernie represents the best of this Jewish call to pursue justice."