Clinton: "Basket of deplorables".
Biden: "Garbage".
HN, all over this thread: "How could people be so stupid?"
In the Democratic Party, there's a long, deep thread of contempt for everyone who doesn't agree. They're supposed to be the party that represents the little guy, but if you're a little guy who thinks abortion is morally wrong, or who doesn't think gay marriage is a good idea, or who doesn't think trans women should be in womens' sports or womens' restrooms, then they don't represent you, and they aren't going to. Instead, they view you as a moral leper, whose only proper action is to repent, and whose culture should be completely eradicated.
If you're on the receiving end of that kind of attitude, it's a fairly normal response to flip them the bird and vote for the other guy.
To all the people who are saying, "how could they be so stupid?", I say: "How could you be so stupid? What did you think was going to happen?"
If you want to win elections, start by not holding in contempt the people you claim to represent. Stop telling them what they're supposed to think, and what they're supposed to value, and what they're supposed to believe. Instead, find out what they think and value and believe, and then represent that.