I'd be shocked if Bernie does vote against Tanden. Yeah, she personally sucks, but why sink her when her replacement won't be nearly as friendly to leftist policy?
I'm undecided and obviously don't have the same information the Senate Democratic Caucus has as to the likeliest alternatives (Bruce Reed could be worse), but this looks like a bad gamble from my view in a way supporting other suboptimal nominees (e.g. Blinken) does not.
Competence and integrity matter and the beliefs she propounds count for little if they be abandoned under the slightest pressure. I could care less about the Twitter drama, but someone who takes bribes (and fails to hide them), busts unions and punches journalists is not the model of a capable Democratic Cabinet member. The wikileaks email in which she allegedly suggests the extortion of Libya could have been a tasteless joke but it looked like a deeply unserious idea proposed in a serious fashion - in other words, Trump-tier policy. Federal government is a tricky business and the last 4 years would suggest it's not well-suited to these.
At least she's a historic pick for representation. Many Cabinet members have failed upwards, but she must be the first to fail upwards through the glass ceiling.