The dirtbag left weighed in a while ago
It's Still Bernie
I think part of the issue is the Dems got used to bringing in Leftist window dressing to pull in the Left votes, then usher the Kucinich, etc. out before the primary, with them endorsing the "centrist" candidate. Sanders was supposed to play this role in the 2016 primary, but everyone was surprised by the amount of support his campaign gained and sustained- the message had traction beyond what they had seen in previous cycles. Leftists actually got their idealistic hopes up.
Democratic Party faithful like to play up how Sanders supporters didn't turn out for Clinton-
when they actually did quite a bit, and more than Clinton supporters turned out to vote for Obama over McCain; and they like to blame Leftists, instead of noting their failure to bring a resonating message that could appeal to the working class and their traditional base to overcome district gerrymandering and the white racist voting bloc.
That's also why a bunch of Democrats aiming for the 2020 presidency are trying on parts of Bernie's progressive platform- they want the voters that are attracted to that message.
Only it's clear almost none of them supported progressive platforms before this, and their voting records won't match their rhetoric.
I'm still of the opinion that the Youth and Left vote are with Bernie if he runs, as opposed to other candidates that mostly have party faithful and nothing else.