Bernie Sanders is not serious about winning the Democratic nomination for POTUS. Sanders does not take advantage of Hillary Clinton’s vulnerabilities. At the most, he is letting the Republicans do it for him; but they are not, not yet. The Republicans are too busy beating up on one another; as Trump has stated “I haven’t even started on Hillary yet.”
It isn’t like there is no material for Bernie; there is plenty. If you are running for office and want garbage on your opponent; Hillary is your man……woman, whatever, prime.
Bernie Sanders acts more like a sparring partner. He is prepping Hillary for the big bout.