Why do so many black Americans support Hillary Clinton? Stockholm Syndrome. They are faithful battered wives. They are yoked to Hillary by co-dependency: “I’ve stuck by you and suffered to do so for so long that you owe me, and I have faith that you will reward me later if I help you reach your goal now.”
In their minds they have no such guarantee from Bernie Sanders (and of course from Hillary such a guarantee is an illusion). It is clear that Bernie Sanders has been successful without being dependent on them up to now. So (again, in their minds) he owes them nothing, and thus cannot be counted on to reward them after the election for their support during it.
What this sad diminished thinking shows is a lack of confident independence, an inability to reason that the best estimator of Bernie Sanders’ future trustworthiness is the consistency of his commitment to their fundamental cause for over half a century.