There is an actual, dedicated Nazi movement in the US. I don't know how many people there actually are involved in it, but it's dozens. Some of them are True Believers and crazy as saints, and some are just hucksters looking for a quick buck.
IMO, they're neither effective, nor dangerous; the honest advocates of white supremacy and Nazi national socialism just show how flawed those ideas were and still are.
The business of "monitoring nazis online" and fundraising on that effort, I strongly suspect, outweighs the actual Nazis by a factor of 10:1 or so.