Hmm....problem is its unclear whether he was indoctrinated into KKK style active white supremecy later in life, or whether he was brought up as just another southerner in a racist culture.
Assuming the former, lets make the POD him not meeting neo nazi types (especially William Luther Pierce) in his teen and collage years. As noted before in the thread he is a chronic attention whore who would both make grandiose claims of his own prowess and achievements, and go out of his way to piss people off (i.e. wearing nazi uniforms in collage and throwing parties on hitlers birthday) and impress those on his side.
Given this, I can almost see him latching onto one of the "edgier" far left parties/causes (communist party, SDS maybe) during collage and pulling the same routine as he did OTL in the white nationalist sphere, all while trying to grab as much money, power, and attention as he could for himself, and probably eventually trying to portray himself as a "moderate" when public opinion turns sharply on the far left.
Whether he gets into any public office depends on whether he would have better luck playing the "moderate reformer" of the far left as he did playing "moderate reformer" of the racist far right.
Honestly though I just want to avoid any TL where he becomes a porn star.
SJW David Duke is far more palatable than Sex God David Duke.
EDIT: That being said, There is an astonishing lack of alternate porn history timelines on this forum, so maybe Porn Star David Duke could be the start of a new trend.