Partisan identities have become increasingly aligned with religious and racial identities. Republicans tend toward Christian and white identities, and Democrats tend toward non-religious and non-white identities. With these highly aligned identities, people tend to be more sensitive to threats from outsiders, reacting with higher levels of anger than those with cross-cutting identities.
Read the whole post. I wanted to excerpt all of it. My one quibble is that I wish that she had not only used Trump supporters as examples of what she is talking about. I think she is saying that people on the left also react angrily to the identity threats posed by those with differing political beliefs and cultural traits, but my guess is that many of the readers of the post will miss that.
I have been interested in the issue of tribalism in politics for quite some time. See, of course, The Three Languages of Politics.