National outrage grew Friday after a self-described Nazi unfurled a swastika flag at Sen. Bernie Sanders' rally at Veterans Memorial Coliseum in Phoenix.

Sanders, who is seeking the Democratic presidential nomination, was joined by at least one lawmaker and anti-hate advocates in condemning the incident, while security at the event faced greater scrutiny.

"It is horrific, beyond disgusting to see that in the United States of America there are people who would show the emblem of Hitler and Nazism," Sanders, an independent from Vermont, told reporters Friday.

Sanders, who is Jewish, had relatives killed in the Holocaust and said he "speaks for the families" of the Americans who died battling "against fascism" during World War II.

The Nazi flag incident was documented in photos and videos posted Thursday night on social media platforms.

Robert Sterkeson, 37, the Glendale man who displayed the swastika, said he had no regrets in an interview with The Arizona Republic Friday. He made ugly references to anti-Semitic conspiracy theories and said Jews should not be allowed to run for president. He also made personally disparaging remarks about Sanders.

Sterkeson said he also attended President Donald Trump's rally in the same arena two weeks earlier. He also made anti-Semitic remarks about Jared Kushner, Trump's son-in-law.

Sanders supporters can be seen tearing the flag from Sterkeson's hands before he bolted from the coliseum. Eyewitnesses told The Republic that Sterkeson held up his middle fingers to the crowd before fleeing.

Sanders did not appear to immediately witness what had happened but told the crowd, "Whoever it was, I think they're a little outnumbered tonight."

In a separate video taken outside the coliseum, a man appearing to be Sterkeson is seen walking away and calling a Sanders' supporter a racial slur. Sterkeson is a self-proclaimed Nazi who has a history of harassing Jewish and Muslim groups.

"This is an appalling display of anti-Semitism against a man whose family perished in the Holocaust," Rep. Ilhan Omar, D-Minn., wrote on Twitter. "And this SAME white nationalist has been harassing the Muslim community for years. Our struggles are tied."

Sanders is the only Jewish 2020 presidential candidate who, if elected, would be the first Jewish president. Recently, Sanders spoke out about the importance of his Jewish heritage, saying it has profoundly impacted him.

Security at the coliseum questioned

The Arizona Department of Public Safety was tasked with security for the event and listed a number of prohibited items, including flags.

Bart Graves, a DPS spokesman, told The Republic Sterkeson clearly violated that rule but said DPS cannot say how Sterkeson smuggled the flag inside.

Sterkeson said no one searched him or his possessions at the event.

"I could have probably jumped up on stage with the guy if I wanted to and draped it around his shoulders if I really felt like it," he said about the flag.

Graves said Sterkeson "saw DPS coming up the stairs to get him and took off in a fury, dropping the flag while he was running away."

Videos of the incident posted on social media show Sanders' supporters yanking the flag from Sterkeson. Other videos show a man appearing to be Sterkeson walking outside the Coliseum after the incident. Graves told The Republic that troopers were not able to locate Sterkeson anywhere on the property and never made contact with him.

"Had we made contact with him, he would've been cited for trespassing," Graves said.

DPS is continuing to look into the situation.

As of Thursday, neither the Sanders' campaign nor former Vice President Joe Biden's presidential campaign have requested Secret Service protection.

Traditionally, candidates initiate the process for Secret Service protection by making a request which must be approved by congressional leaders and the Department of Homeland Security.

On Tuesday night, protesters rushed the stage of a Biden campaign event but never reached him; his wife, Jill Biden, helped stop them.

Nazi flag a sign of anti-Semitism on rise

There were 1,879 recorded anti-Semitic incidents in the United States in 2018, a near-historic high, according to the Anti-Defamation League, an anti-hate organization.

Oren Segal, vice president of ADL's Center on Extremism, told The Republic that anti-Semitism is not unique to any one political movement or ideology

"I've been doing this work for 20 years. The tropes and narratives that would be common for me to see on some fringe platforms when I first started now appear to be part of the day-to-day messaging and narratives that we see, whether on Facebook or cable news," Segal said. "That's what is disturbing because I'm not sure people recognize anti-Semitism anymore because it's so ubiquitous."

At the deadly August 2017 "Unite the Right" rally in Charlottesville, Virginia, neo-Nazi marchers waved swastika flags and shouted "Sieg Heil" and "Jews will not replace us." A woman was killed when a white supremacist drove his car into counterprotesters.

An Oct. 27, 2018, mass shooting at the Tree of Life synagogue in Pittsburgh killed 11 congregants and wounded six others.

To Segal, the Thursday night incident at the Sanders rally in Phoenix is a reminder that anti-Semitism is alive and well among us.

"The image of the Nazi flag above Sanders during his speech was chilling not only because of the visual but because in 2020 an individual felt comfortable enough to bring a Nazi flag into a rally of a legitimate presidential hopeful," Segal said.

David Harris, chief executive officer of the American Jewish Committee, said that he was heartened to see the crowd's quick response against Sterkeson and the flag.

"One person held the flag and countless people booed and showed their complete disgust," he said.

Harris said he wants people to know that anti-Semitism is not just a threat to the Jewish community but to all Americans.

"Don't ignore it. Don't look the other way," he said, "Confront it and understand that it threatens everything that America stands for: democracy, pluralism, mutual respect and the rule of law.

"This was an attack on Bernie, but ultimately it is an attack on all of us as Americans and we need to stand against it."

Savannah Behrmann of USA TODAY contributed to this story.