This was posted somewhere else here on a conspiracy thread you should show it to him. Mitchell and Webb clear things up completely.
Your dad is just pranking you. However, it could be fun to stage a fake intervention as if you thought he really was losing his marbles. Get someone to play a health care worker to come to his home to evaluate him. They should speak to him like his mind is going soft and try to calm him down when he gets angry. Start mailing your mom brochures for assisted living facilities and have her leave them out for him to find. Bonus points if you all act like supporting Trump really was a listed sign of dementia.
I asked him when he first brought it up in the car. He seemed completely puzzled by the fact that I questioned the validity of what he saw without having actually watched it myself. The next day, I overhead my mom telling him to “stop watching that trash” when he was on the computer in his den.
I think he’s just bored and is watching this b.s. out of curiosity. Ironically, he was very concerned in the past that my kids were “spending too much time on the computer” when they were young.
Ugh. Nothing good comes with old age… 
Thanksgiving Dinner one of my gf’s elderly aunties was talking about the healthcare crisis and giving examples of how it affects her. During a lull in conversation, I opined, “Well, President Trump will fix all that”.
At his peak, Letterman never got such laughs.
Maybe dad is just fucking around.
Whats the record for off topic projections?
You sure? I could have sworn it was the Chinese…huh
Or you could all pretend to start supporting Trump yourselves and see how he reacts.
Your dad is entitled to pull your leg even if it’s not something he usually does. Leave the doctors out of this, for Og’s sake.
The only joke my dad ever told me was when I asked him what the combination to the PO Box was. He said “Let me give you a little aid.” I waited and waited… he finally said “That’s the combination.” A-I-D.