Briahna Joy Gray, Sanders’s national press secretary, tweeted [shade] about the Warren campaign’s unionizing effort, which is still under contract negotiation. 

…In another tweet, Gray criticized Warren for not supporting a national rent control initiative.

…The campaign’s official position is that their primary focus is going after Joe Biden, as Sanders’s pollster Ben Tulchin told Huffpost, sharing a text message script aimed at persuading Biden voters. But several members of Sanders’s team haven’t been sticking to that same script.

Sanders campaign: Top staffers make a case against Elizabeth Warren – Vox

This is just of the reasons that many Democrats, from rank-and-file to insiders, do not trust the Sander’s organization: his inability to stick to and control the message of his staff and supporters. They go negative and adversarial and he does not reign them in.