Oddly enough, I don't think there's much left he can say to alienate anyone else left in his base. He could come out and say the Confederate flag should be the new American flag and I don't think he'd lose any votes. I don't know what he could say that would turn off his voters. I think the voters that can be turned off by him are already gone. The ones left will justify anything he does.
That being said, the election is a ways off and anything can happen. Sure looks like Biden has it locked up, but I will never say never until it's over. Biden's handlers have been very smart keeping him under wraps as much as possible. If it ain't broke, don't fix it.