Do you have any source confirming that he is a registered Democrat?
I’ve glanced through his writings (his website is down, but there are cached versions around), and he attacks both sides pretty hard (he goes after “neocons,” but he also viciously attacks liberals, marxists, and Democrats).
As much as some would like to make this guy into a far-left Democrat, I wouldn’t call him a left-wing whacko OR a right-wing whacko. I think it’s sufficient quite simply to call him a wacko.
Democrats founded the KKK, after all.