Sometimes people just need to be written off. I am afraid you are right. For some inexplicable reason, my father became a rabid liberal. Maybe because it was his time to be ordered how to vote by the AARP, maybe because it was his turn at the trough, but for whatever reason, it became impossible to communicate with him at all.
I was sickened that a WWII Veteran had become such a leftist, and I am still sad that I did not speak to him the last two years of his life, but that seemed the be what he wanted.
My last words were, "If I wanted to hear that stuff, I would subscribe to the Boston Globe!"
That is sad about your father. Maybe there is some kind of connection between senility and liberalism. I don't know. I have been very blessed by my parents. They are conservative Republicans and pretty outspoken about it too. They have an antique shop and play Rush Limbaugh's radio show in it. A few times some of their customers might complain about Rush or something he says and if the customers are being obnoxious about it my Dad just tells them to "Hit the road!" My husband had to deal with Democrat parents and I could see his agony trying to reason with them when there was just no reason to be found in them. Eventually his Dad came to the party but his mother was senile by that time. A sad way to end up.