i would guess that a part of the reason that sanders does so poorly with black voters is that he reminds them of the activists in the 60s that they were taught to reject, and ultimately did, under the guidance of the religious authorities.

what happened to this movement? it was suppressed, but it ultimately got abandoned and rejected. and, by who? the people that sanders is trying to get to vote for him.

so, invoking this stuff is probably hurting him more than it's helping him.