Tom.... I don't know if you honestly don't know this or if you're just playing dumb because it suits your cause....
but this is exactly what the FBI has done to the Klan over the past few decades. They are no longer a meaningful movement, but instead are a rag-tag bunch of small and mostly inconsequential groups of morons. You haven't heard of this group because the group consists of about a dozen people in rural Michigan. They occasionally try and use the internet to coordinate with other inconsequential groups and this is most often how they are caught.
Here... From that bastion of right-wing thought... the ADL
https://www.adl.org/education/resources/...of-the-kkk
Despite a persistent ability to attract media attention, organized Ku Klux Klan groups are actually continuing a long-term trend of decline. They remain a collection of mostly small, disjointed groups that continually change in name and leadership. Down slightly from a year ago, there are currently just over thirty active Klan groups in the United States, most of them very small. However, the association of Klan members with criminal activity has remained consistent.
So 30 very small groups spread across a country of 350mm people... and under almost constant surveillance by the FBI.
I don't know how many people that is, but according to wiki, the same source I quoted above says that in 1999, there were just over 100 groups with no more than a few thousand members. If you cut the number of groups by 2/3rds, you're likely speaking of 1/3 of 'no more than a few thousand' people.... so likely just a few hundred. Also according to wiki, the SPLC (another right wing think-tank) agrees that its about 30 small groups as of 2017.