It worries me actually, makes me sad too, since my family is all infected. My mother visited yesterday and said she wanted to watch MSNBC so she could see if Trump had been killed yet. My whole family is similarly afflicted. I recall during GWB, they didnt like him at all, but the level of loathing for Trump is 10x worse. It is irrational, and worrisome.
Initially well meaning, but not original thinkers, get easily swayed by the morning and evening "social" shows which are nothing but unmitigated, relentless hate filled screed and propaganda.
If you value their kinship, get into serious but polite conversation, and ask them why they support the ideas, pick one, and dismantle it piece by piece.
If you don't values the kinship, walk away
The real difficulty dealing with family members who are TDS is their abject stupidity and thorough ignorance. I plan to ask them if they will return their pay check increase.
You cannot argue with stupid and there is only so much you can teach ignorant. What you can do is condemn their facts as really dumb and based on lies.