I suppose there's value in the horseshoe theory in that both Trump and Bernie supporters are wholesale disdained by nearly everyone else. But whereas Trump's supporters are hooting suburban dads in Rascal scooters, Bernie's are generally service employees, teachers, and other working class people. And the disdain shown for them by supporters of other candidates just reeks of protecting upper or upper middle class interests. Whether by painting them as uneducated or otherwise ignorant or shortsighted, I suppose it's easier to attack the supporters than attack the candidate.
The caricature of Bernie is an angry old man but I think where criticizing him falls apart is that the temper tantrum he's throwing is over children living in poverty or people dying from not being able to afford insulin.
I find myself defending him here even though he's not my favorite candidate because the arguments against him here are so obnoxious.