on the one hand, this is a safe tactic, because almost nobody supporting sanders is going to care one way or the other.
on the other hand, it's gutter politics - because it isn't designed to win votes so much as it's designed to suppress turnout. see, that's what he needs right now, though. he's not going to swing these wealthy new york minorities that came to america to break it big and don't want to pay taxes to fund health care for poor people. but, he could conceivably disgust them enough that they get disinterested and apathetic.
hey, if you want to play the game, you want to win it. and, he's literally got millions of people that can't vote for him. i'm more inclined to suggest it's too little, too late - but also that it's a valid tactic going into pennsylvania.
but, it's also another implication that sanders doesn't plan to concede any time soon.
https://en.wikipedia.org/wiki/Nouveau_riche