In this so-called 'relationship', the black voting bloc is what counts. Period. Don't think that 8 years of Obama in the WH hasn't awoken people to that fact. Your man isn't entitled to shit. He can get off his ass and earn the vote, or someone else will.
To Sanders' credit, he seems to be getting it now, big-time. Shame so many of his supports are acting like assclowns and demanding that black people sit down, shut up, and take a backseat to economic (ie. their) issues instead, then engaging in temper tantrums online. That's a huge turn-off, and one that's hurting the very person you're purporting to support.
Let me be clear.
You're being told, "no".
You've been given the reasons why.
You want your man to win? Start listening. Or wither on the vine. That's the great thing about politicians, there will always be another one to take that spot.