I know this. The KKK, or at least a great many chapters, is an organization that helped coordinate crime. By this, I mean that hierarchical members of the KKK organized criminal acts to be perpetrated by other members of the organization in their hierarchical control. The KKK was 100% a criminal organization that could have been prosectured using RICO. It would not even have been the only overtly political group where this would have been done.
There's a lot of reading you can do about why RICO isn't routinely deployed against ideological white supremacist organizations (including those that refer to themselves as "KKK"). RICO is deployed against organized white supremacist criminal gangs, where there's a centralized "enterprise" and a pattern, rather than a scattering, of racketeering-predicate crimes.
I always wonder what people are thinking when they suggest that the US could silence an entire viewpoint through invocation of RICO or FTO designation. If the government could have declared an entire line of thought illegal, don't people think we would have done so numerous times already? We couldn't even ban membership in the actual communist party at the height of the Cold War (not for lack of trying, though).
It's a 100 organizations with 10-30 members who believe they're the true heirs to the KKK. It's be very similar to trying to arrest the head of the Nazi party. There really isn't one.
