Do they realize that four more years of Trump would mean that the supreme court will probably end up with a 7-2 conservative majority for many years to come? And that this would destroy any progress on the climate and any other important matter?
Four more years of Trump is unacceptable...
For the most part, they fully understand the disaster that Trump represents.
I would liken the situation to a game of chicken. Every cycle, corporate Democrats give progressives the same choice. A corporate Democrat who gives them nothing or a disastrous Republican.
As long as progressives go along, the corporate Democrats control everything and yield nothing to progressives. Progressives have no power other than their ability to veto the corporate Democrat.
For the poor American youth who can't afford to buy a home, raise a family, are looking forward to climate Armageddon and drowning in student debt, they are looking at a disaster w/o significant relief. If the corporate Democrats are unwilling to meet them halfway, then they don't have as much to lose from a Trump presidency. They already have a disaster.
If would be the height of stupidity for the young progressives to hand over their votes w/o gaining something in return. They are 40% of the Democratic Party electorate and they have zero power in the Democratic Party. It's Biden's job to move in their direction.
There is an african proverb that goes something like this:
"If the village does not embrace the child, the child will set the village on fire and bask in the warmth".
The child is America's young and poor. The village is the Democratic establishment. Trump is the fire.
Not sure if you are American, but the plight of America's working poor is crappy and increasingly desperate.