Historically unpopular Trump can still be reelected.

This seems pretty accurate to me. I'm not an expert on party dynamics, so I don't fully understand why this happens to be the time some choose to fight for the heart of the Democratic Party instead of thinking strategically about winning the next election.

It could be that losing sometimes causes an organisation to engage in soul-searching to turn things around (if they are what organisational theorists call a "learning organisation," e.g., one that tries to learn from its mistakes). But it's not clear that the lesson from Hillary's popular vote win and EC loss that can be traced to GOTV(Get Out The Vote) failure in a handful of counties is to make a large ideological shift.

It could be that the left-wing of the Dems mistakenly believes that the American public really agrees with them. If you stay in a bubble and ignore survey data you'll believe all kinds of weird nonsense.

But my fear is that Trump's support on the left intuitively senses populist momentum in the US and wants to capitalise on it, offering an alternative populism. This is dangerous because populism wins by pretending to be more democratic, by attacking the elites and the system, but at its core it is anti-democratic because of its insistence that those who support it are the real demos, and only them, regardless of their size. Populism is ultimately just a deviant variety of nationalism that thrives on distinguishing between the real us and the fake us, who are actually an untrustworthy not-us.

And the not-us, regardless of their size, can have no legitimate concerns of which we need to take notice in our policy-making. They are, in fact, so dangerous that they need to be shut out of the policy-making process entirely, their voices quelled, and their electoral participation prevented lest they unjustly regain control and thwart "true" democracy.

The Democrats left-wing pose as an alternative to Trump, but they are actually just a different wing of the Trumpian populist party.