In the spring of 2016, Brian Levin found himself in an uncomfortable position: trying to save the life of a Ku Klux Klan member.

Levin, a former New York City cop who studies domestic extremism as the director of the Center for the Study of Hate and Extremism at California State University, was documenting a Klan rally in Anaheim, California, when a counterprotest suddenly took a violent swing — forcing Levin to physically place himself between a Klansman and a furious, anti-fascist mob that seemed ready to kill.

It made Levin wonder if in his focus on the obvious subject — the white supremacists — he’d overlooked a growing source of extremism: the far left. “At that point, I said we have something coalescing on the hard left,” Levin told VICE News.