The GOP doesn't think they are fascists. They think the term is only being used to try to deride them without actually being correct. From there, when they see "Anti-fascists" constantly opposing THEM, they think it's just some violent group that has used an ad hominem attack for their name.

It would be comparable to someone making an anti-shithead group, and then that group is always out trying to stop you from doing whatever you do. Not only would they be a direct problem for you, but the fact that they're targeting you would imply then that they're also calling you a shithead.