The failures of the 1970s; the emergence of Clinton's "ignore my character, I'll give you what you want" deal; dividing the center/left coalition in the face of Trump; the party's takeover by too many young activists. If you can't see how the Dems also failed, I can't spend Sunday explaining it.
"a party whose excesses and feckless decisions also had a lot to do with the rise of authoritarian populism. (Populism was once a thing among the Democrats.)" can you expand on that? Because that sounds an awful lot like "baby boomer bothsidesing".