And I'd say the change has happened at least somewhat in the Democratic leadership - in many of the presidential candidates, even if not in the House and Senate leadership.

And I'd argue that this change was going on before, but you didn't see it, because of Obama. He, in one person, was the face of the Democratic party, and that hid what was going on underneath. As you say, Obama was not on the left, and because he was the public symbol of the party, it was easy to not see the left growing.

Was Obama to the left of Clinton? I could accept "no" as the answer. But was the median Democratic politician during Obama to the left of the median Democratic politician during Clinton? To me, it appears that the answer is "yes".

I don't think that abandoning the working class is something that just happened in the last 2-4 years. I could even argue that it happened under Clinton, but he had the political savvy to hide it. It was probably there, and growing, under Obama. It became glaringly apparent under Hillary, when she had no interest in even talking about the working class, and Trump did. That's what changed in the last 2-4 (let's call it 3) years - Trump stole what the Democrats thought was "their" issue, so solidly "theirs" that it didn't even need to be mentioned.