The Democratic Party is not some sort of religious sect, it's a political party. Viewing it as a type of religion, as keepers of the Truth (with a capital "T") while opponents are evil heretics is both wrong and dangerous and is a direct threat to the liberal tradition that we all say we believe in. And yes, substitute Republican for Democrat and this type of thinking occurs as well. This is not just one party doing this. Too many good people - and they are good people - on both sides think like this. Trump has made it worse but it didn't start with him and won't end when he leaves.
This type of thinking, this quasi-Manichaean worldview, is why in large part the country is so divided (although I'm not sure among "ordinary" folks the divisions are so great; at least I hope not). Each side views the other as simply evil, as malevolent, as members of a dangerous tribe that must be destroyed. They have no legitimate point of view and any accommodation with them is a compromise with evil. This destroys the "liberal tradition" that has worked, that has helped us make a better country (and world). The US had done some terrible things; but we've tried to fix them.
Good grief, we have to stop this type of thinking. It'll destroy us.