Usually, you can't change your parents that much. Many of us, from all kinds of different political and religious groups, try to change our parents, but I can say from experience that it often is impossible, though not always. Where it is possible to change your parents, it takes a lot of time and hard work, and many times it's painful.
Face it: however brain dead they may seem to you, your mother remembers the pain of giving birth to you after 9 months of pregnancy. Your mom and your dad helped you through potty training, kept you fed and safe while you were reaching adulthood, put up with you when you were going through the pains of puberty, and probably cared for you at times when you were sick, sad, angry, frightened, etc.
They're going to remember all of this while you're talking to them about politics. Probably they're going to write off whatever you say because they think they know better and because they think you "owe them" from raising you. Probably they still think of you as a child who doesn't know much and who needs their "superior" wisdom. And I can say from experience it's really hard to change that -- no matter how old and smart and successful you may get. In their minds, you're still their little kid.
I totally agree with you that Trump and the GOP are awful, if that's what you truly believe and you're not just a pro-trump Troll trying to fool us. But I'd give up trying to change your parents, if I were you.
Just keep quiet and be as polite to them as you can be, hold fast to what you have found to be moral & true, and realize that when you're out of their house, you'll have the freedom of say and think whatever you want. You can love them and be grateful to them for all they've done, and still think they're wrong about politics. And that's okay. Whether or not they ever accept your ideas about the subject.
-- democratic socialist for bernie sanders' ideas going forward