Sibling drama

My brothers and I are all
in our 60s. We've mostly gone without
a huge amount of drama-until recently. My older brother(A)is a conservative, my younger brother(B)and I are both liberals. A and I are close, and we have an understanding to not talk politics. B has always been a force unto himself, he's a provocateur, likes arguments. B sent a news story on an eminent domain case that destroyed a black neighborhood to A, who responded by demanding that we never discuss liberal politics because it made his heart race and his blood pressure soar. This all ended in brother B calling brother A a fascist and they haven't spoken since.

Now I know this comes from brother A's relationship with our father who was a hugely liberal guy, and a narcissist pain in the ass who belittled him for holding certain views. However-our father has been dead for nearly two decades, and none of us have lived under his roof since the 1980s. I kind of feel like, you're 68 years old, it's time to stop hearing his voice in your head. I don't understand how your grip on your belief system is so tenuous that a conversation involving a different viewpoint sends you into panic mode, and all you hear is a long dead person yaking in your head. At the same time, brother B is a pain in the ass who lives in an alternate reality where he thinks things happened one way, even if all the proof is to the contrary.