Democrats are worried about Bernie's sudden polling surge in the lead-up to the Iowa caucuses. Writing at CNN Politics, Chris Cillizza spelled out what seems to be happening:

With the Iowa caucuses now less than a month away, a realization is setting in among the political class: Bernie Sanders has a very credible chance at winning the 2020 Democratic nomination.

The problem is that even if Bernie excites the base, which is the secret to winning in the primaries, it's highly unlikely that he will excite the broader American population. An AP article described the outright "fear" among establishment Democrats that Bernie might become their candidate:

Increasingly alarmed that Bernie Sanders could become their party's presidential nominee, establishment-minded Democrats are warning primary voters that the self-described democratic socialist would struggle to defeat President Donald Trump and hurt the party's chances in premier House, Senate and governors' races. [snip] "You need a candidate with a message that can help us win swing voters in battleground states," [Rahm] Emanuel said in an interview. "The degree of difficulty dramatically increases under a Bernie Sanders candidacy. It just gets a lot harder." [snip] Less than four weeks before Iowa's Feb. 3 caucuses, Sanders' critics are making a concerted effort to turn up the volume.

One Democrat institution that's trying hard to turn up the volume is CNN, as it demonstrated during Tuesday's debate. The most noted example of CNN's bias occurred when moderator Abby Phillip asked Bernie a loaded question that assumed facts not in evidence:

CNN reported yesterday — and Senator Sanders, Senator Warren confirmed in a statement — that, in 2018, you told her you did not believe that a woman could win the election. Why did you say that? (Emphasis added.)

Bernie firmly denied saying any such thing and explained why it was risible to believe he did. After he ended by reaffirming his denial in response to Phillip's final request for clarification, Phillip, without missing a beat, turned to Warren and asked, "Senator Warren, what did you think when Senator Sanders told you a woman could not win the election?"

If there was any doubt that Phillip's behavior was part of an intentional course of conduct on CNN's part, one only needs to look at some of the screen chyrons that ran during the debate:

Democrats are now crying foul. Matt Taibbi savaged CNN for abandoning objective reporting before, during, and after the debate:

Over a 24-hour period before, during, and after the debate, CNN bid farewell to what remained of its reputation as a nonpolitical actor via a remarkable stretch of factually dubious reporting, bent commentary, and heavy-handed messaging.

Newsweek wasn't far behind:

The biggest loser from Tuesday's Democratic debate was CNN's journalistic credibility. CNN debates have been marked by a tendency to pit one candidate against another, American Gladiators–style, so it's no surprise that the cable network took its own journalistically dubious "scoop" — about Bernie Sanders allegedly telling Elizabeth Warren in 2018 that "he did not believe a woman could win" a race against Donald Trump. ... But it was less predictable that CNN would frame those questions in such a nakedly one-sided manner, with wording that presumed that the truth was known about what was really said in a disputed, year-old private conversation.

Similar articles could be found from the AP, the Hill, and Morning Joe.

In 2016, the establishment not only thought it was Hillary's turn, but also believed that Bernie didn't have a snowball's chance of winning. In 2020, the establishment doesn't know whose turn it is, but it's darn sure that it's not Bernie's.

It remains to be seen whether, if the establishment blocks his chances a second time, Bernie's supporters will slink away angrily this time, as they did the last time, or if they'll turn the Democrat convention into a rerun of the 1968 Chicago convention.