The ill-informed and self-important commenting gratuitously on things beyond his understanding.
The bitter irony is that if establishment Dems hadn’t torpedoed Bernie he might be just about to stand down after a second term with his marbles still intact.
Of course, Bernie might have made a mess of it. We well-meaning lefties sometimes do, but if he had he would have been kicked out in 2020 and left, perhaps grumpily but without inciting insurrection.