He's not?
His loud affirmations of Trump, along with his mania about "Jewish supremacism," and the convenient brush he makes to tar all of us with, and he's "certainly not a tool of the left?" Even the Birch Society didn't like this guy!
Then there's his evolutionism, of course, but some people don't seem to think that's important.
David Duke is a flake, and indeed a tool of the left. Why else was he previously palling around with the likes of Cindy Sheehan and Code Pink? Duke is much like the late Fred Phelps, a disinformation operative to slander conservatives, much like the way Phelps slandered Christians.