It's not necessarily as simple as actual mutual hatred. That only explains a fraction of his votes.

His voters want to believe that if something is okay for the president, then it's okay for them, even if it's not.

All his voters have "bone spurs" of some kind, so they want to enable people with "bone spurs", and vote for Mr.Bone Spurs, even if trump would gladly fire someone for having "bone spurs".

They hate everyone else and he hates everyone else, so they feel represented, even if he hates them. What good has he ever done for the demographic that voted for him and paid his bills? Absolutely nothing. It's one big ass grift.

That also turns it into a sunken cost fallacy for a lot of them. They lie to themselves, because they're too vain and afraid to face their mistake. The extremism plays into this as well. Once you cross a point of what is normal morality, it gets considerably harder to walk back from there.

If Trump really hates immigrants, then why does he keep hiring them at Mar-a-Lago? The answer is simple: money. He has absolutely no interest in cutting off the supply of cheap workers. The extremely expensive wall construction also didn't work in any meaningful way.

The only thing he did successfully was to rile up a lot of angry people just to collect their money.