My mother's become like that in recent years, but my sisters and I are almost grown so we don't mind. Have you tried telling your father, or your mother or some other adult you trust, that he's frightening you? There are reasons adult topics are not discussed in front of children.
You might attempt to explain to your father that being pushed into politics will not make you agree with him. If anything, you'll probably disagree with him simply because you were pushed into it. If he is mature enough to understand that, he will tone down the loud discussions.
