I guess you fail to see the dichotomy between the two groups. White Supremacists run on the GOP ticket all the time. They currently support the party's standard-bearer; who, for his part, does little to dissuade them. Duke most recently ran for a GOP senate seat. Here in CO, GOP-endorsed candidates have been forced to walk away from their campaigns after being publically outed and the chair of the Delta County GOP openly posted a racist meme comparing Obama to a monkey. 

You don't see that with Antifa. Despicable as their actions are, they aren't encouraged and emboldened enough to run for party seats. In all likelihood, they despise Democrats because they are too moderate. I'm not saying all, or even the majority of Republicans are racist. What I am saying - and what is getting harder to deny with each passing day - is that the GOP cynically courts the vote of racists... to the point that they feel confident enough to run on the party ticket and participate in party events.