During the first presidential debate on Tuesday night, when moderator Chris Wallace asked President Donald Trump if he would be “willing, tonight, to condemn white supremacists and militia groups, and to say that they need to stand down,” the President seemed to many to do the opposite.

“Proud Boys,” he said, “stand back and stand by.”

While it wouldn’t be the first time the President failed to condemn white supremacists, his most recent comment—directed at an organization founded in New York City during the 2016 presidential election season and designated a hate group by the Southern Poverty Law Center—confused even members of his own party. On Wednesday morning, Tim Scott, a Black Republican U.S. Senator from South Carolina, told reporters that he thought the President “misspoke” and “should correct it.”

Speaking to reporters later that day, Trump indeed walked back his comments, asserting that he did not even know of the Proud Boys before former Vice President Joe Biden mentioned them in the debate as an example of a militia group. (At least one outlet has linked former Trump adviser Roger Stone to the group, and President Trump’s FBI has called them an “extremist group.”)

Members of the Proud Boys, however, saw his remarks differently, celebrating online and vowing to stand by, an expert monitoring their social media posts told TIME. On Twitter, Kathleen Belew, author of Bring the War Home: The White Power Movement and Paramilitary America and an assistant professor of History at the University of Chicago, warned that such an interpretation was no surprise: Trump’s shout-out sounded like a call to arms, she wrote—a “green light” that could be “catastrophic.”