So this is a "I've decided I hate you and there's nothing you can say to change that" situation? You know you'd have an easier time if you stuck to attacking your enemies?
He's cowardly backed away from all debates. Him saying this doesn't mean this has changed. It's just posturing. He never would have an actual fair head-to-head debate with Biden. He'll either say anything fair is unfair so he won't participate or hell say he can't make it for some reason.