There are a few elements at play here.
First is the abject shock of such a big loss. The Democrats (and particularly the hardcore sub-group Regressive Left) were absolutely convinced that Obama's wins were The Turning Point for the country. They figured that our changing demographics were in part responsible for those wins, and had progressed to a point at which they'd take the party from here.
Second is Trump and his behaviors, which essentially rub salt in the wound. His loud, hyperbolic, simplistic, buffoonish behaviors made this unexpected loss much tougher to swallow. That's exacerbated by the way Trump's fans have so gleefully ignored so much about him.
And, I suspect, third is the fact that, at some level, they realize they played a role in his win with their own behaviors. This was the ultimate (and perhaps one-time) large-scale pushback against Political Correctness and Identity Politics, strategies on which leftists have hung their hat for so long..
1.) You could overcome some of the defects in your argument by distinguishing between "loss for Democrats" and "loss for the country". Why you don't remains a mystery.
2.) "Trump and his behaviors" isn't just rubbing salt in the wound - it's all part of diminishing the Office of the Presidency and the standing of the U.S. Administration to the status of, essentially, a clown parade of incompetents, grifters and crooks - just after President Obama had restored his office to a level of decency and reasonableness after it had been nearly destroyed by his predecessor. Which again points to the necessary distinction, as mentioned above, you fail to make.
3.) Yeah, that's the old canard of "identity politics" by the regressive right, thrown out to cover up their racist, (White) identity politics. Seeing you rebleat same is kind of disappointing. The largely leftist hope of seeing the American birth defect at least diminished, groups (other than ******) recognized along with their specific life situation and needs, and the insistence that all be treated with equal respect, may have had some influence on the 2016 election. The blame for that, however, doesn't show up on the side of the Left by any reasonable standard. It shows up on the side that would cling to their supremacism and racism, and vote accordingly.
But thanks for being somewhat more specific while riding your shtick. Much appreciated.