Third option: dedicated Republicans can also be negotiated with. You can trade off, as above, or adjust numbers.
If you think that Trump is uniquely bad, you can compromise with the dedicated Republicans on non-Trump parts of their agenda. Tax breaks or deregulation.
But just assuming that every Trump voter is a White Supremacist is no good.
If 46% of the country were _actuality_ White Supremacists, they would have a commanding plurality in Congress. Everyone would have to suck up to them. They would be way better at pushing their agenda.
So let's start with the why: I think these fall into roughly three categories.
First: People who actually like Trump's policies.
Second: People who always vote Republican.
Third: People who felt Trump was better than Clinton or Biden.