How worried can Democrats be about their 2020 prospects? After all, incumbent president Donald Trump trails all of their leading candidates in nearly every poll. And now CNN reports that their purportedly most electable candidate has experienced a sudden — and perhaps inexplicable — renaissance in the polls:

Former Vice President Joe Biden’s lead in the race for the Democratic nomination for president has rebounded, and now stands at its widest margin since April, according to a new CNN poll conducted by SSRS.

Biden has the support of 34% of Democratic and Democratic-leaning registered voters, his best showing in CNN polling since just after his campaign’s formal launch on April 25.

Sens. Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont are about even for second, with 19% and 16%, respectively. Behind them, South Bend, Indiana, Mayor Pete Buttigieg and Sen. Kamala Harris of California each have 6% support, with Sen. Amy Klobuchar of Minnesota and former Texas Congressman Beto O’Rourke each at 3%.

CNN’s poll is not the only evidence of a Biden bump, although whether it’s meaningful is another question. Since August, Biden’s RCP average has oscillated between 26-30%, and even with this CNN poll factored in, it’s only at the top of that oscillation. The most recent results from Morning Consult (30%) and Survey USA (32%) put Biden over that oscillation curve, but again not by much, and no one knows for how long either.

A better question might be what transpired to give Biden such a big jolt upward in the CNN series. Literally nothing comes to mind. He didn’t have a good debate last week, although he didn’t have a disaster either. Biden-mentum is almost a joke at this point, and his fundraising has become second-tier. The only good explanation is that Democratic anxiety over the prospect of a radical progressive takeover has refocused voters on Biden as the most marketable moderate:

When the 2020 Democratic presidential contest kicked off earlier this year, the massive field was hailed as the most diverse in history, with candidates who spanned the ideological spectrum and offered enough in a broad buffet of options to excite any voter. But after 10 months of campaigning and 15 hours of nationally televised debates, another emotion is rising: anxiety.

Party leaders and activists are citing weakness in all of the leading contenders, including former vice president Joe Biden, who has been forced on the defensive about his family’s ethics, performed haltingly in debates and set off alarms with his poor fundraising. They also fret that the two other top-ranking candidates, Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.), are too liberal to win a general election. Other candidates have had moments to shine, but none yet have fully transformed that into anything approaching momentum.

Oprah Winfrey, an early backer of Barack Obama who was initially enthusiastic about former Texas congressman Beto O’Rourke, has repeatedly begged Disney chief executive Bob Iger to jump into the race. Hillary Clinton, according to two people close to her, has not ruled out jumping in herself, a sign that she is hearing similar dissatisfaction. …

John Coale, a major donor to both Bill and Hillary Clinton, was more blunt. “They don’t have anybody who can win the general [election],” he said.

Again, this is a strange claim to make when polling shows the opposite. RCP doesn’t chart all of the results for all of the combinations, but you’d be hard pressed to find an argument against electability for any of the current crop of Democrats. Biden has only trailed Trump in one national poll all year — a Rasmussen poll. Warren has only trailed in a few, and none since July. Sanders has only trailed in two, although one was an Emerson poll last month. Even Buttigieg has more or less split the polling with Trump.

Of course, Trump voters don’t tend to trust the polls, and 2016’s election more or less vindicated that point of view. Perhaps Democrats have lost faith in them too, which might be a big signal. For the moment, though, it’s the only semi-objective evidence at hand.

So who’s stirring up all this anxiety? Cui bono? The Hill pooh-poohs the idea that Hillary Clinton is working on a comeback, calling it a “Republican fantasy,” but it’s veeeerrrry interesting that all this “rising anxiety” seems to be coming from the Democratic establishment. One has to wonder whether the dismissal of the entire field isn’t just a machination to generate a late draft-Hillary movement. That in itself might explain any lasting Biden bump that could be emerging.