On Thursday, a man was forcibly removed from a Sanders rally after he unfurled a flag with a swastika on it. The crowd immediately booed the man. Members of the audience swiftly ripped the flag from the individual’s hand, and the individual was removed quickly by security.

Sanders recalled the incident on Sunday during an interview with CNN. He learned about it after leaving the stage. The incident sparked an outcry, was widely criticized on social media and prompted calls for increased security.

“He was behind me. And I was speaking to the crowd, and I saw crowds booing, and I turned around, I didn’t quite see what it was. I learned about it right after I left the stage,” Sanders recalled. “The idea that there was a swastika, a symbol of everything that this country stands against — we lost 400,000 people fighting that symbol, fighting Nazism. Six million Jews were killed, other people were killed. The most devastating war in the history of humanity.”

Sanders would be America’s first Jewish president if elected. Sanders’ extended family from Poland were massacred in the Holocaust during World War II. 

This fact was referenced in a tweet from former Vice President Joe Biden, who is also a Democratic presidential candidate and competing against Sanders.

Biden condemned the act, referring to it as “disgusting and beyond the pale.”

The incident puts extra scrutiny on the upcoming Michigan primary.

Sanders and Biden were both touting potentially influential endorsements from black Democrats on Sunday. California Sen. Kamala Harris, a one-time 2020 presidential candidate, announced her support for the former vice president and planned to campaign with him Monday night in Detroit.

Meanwhile, 1988 Democratic presidential candidate Rev. Jesse Jackson Sr. endorsed Sanders and appeared with him in a rally at Grand Rapids on Sunday.