“Swing states have a higher concentration of swing voters. We need a nominee who draws them to the Democratic column,” said Rahm Emanuel, the former Chicago mayor and chief of staff to Obama. “Sanders’ theory, like Trump’s for the right, is based on the notion of a higher turnout of infrequent voters.”

Sanders is in a strong position, based on recent polls, to win Iowa and then New Hampshire. A one-two punch in the first two states could make him hard to stop. Joe Biden’s firewall — his popularity among African-Americans in South Carolina and other Southern states — would face a severe test.

But the Democratic establishment is caught in a catch-22: Attack Sanders and risk galvanizing his supporters and turning him into a martyr of the far-left. Or leave him alone and watch him continue to gather momentum.

Their bind unfolded in plain sight last week when Hillary Clinton complained that “nobody likes” Sanders and wouldn’t initially commit to backing him if he were the nominee. (She later clarified that she would do so.) Clinton suffered a backlash, and Sanders’ has only gained strength in recent days.

That’s largely why Bennett’s push for organized opposition to Sanders isn’t gaining traction.

“We’re not wanting to put our finger on the scale in any way,” said a board member of Priorities USA, the Democrats’ largest super PAC.

Sanders struggled to break out in polls for months in 2019 as fellow progressive Elizabeth Warren mounted a strong campaign. But Warren regressed after she was besieged with questions over how she would pay for Medicare for All — ironically Sanders’ signature issue, but over which he had not been pressed for similar specifics, critics said. (Last week, he again gave a vague answer about its costs to CBS’ Norah O’Donnell.)

Bennett blamed the media for not holding Sanders to the same standard as Warren.

“They let him get away with murder,” he said. “They let him bluster past hard questions.”

Sanders campaign officials did not initially respond to requests for comment. After publication, campaign manager Faiz Shakir said in a statement to POLITICO, “Let’s be clear: our growing support results from working-class Americans from diverse backgrounds demanding an agenda that transforms our country."

Shakir added: "All Democrats should be ecstatic to witness this movement attracting new supporters. To win seats up and down the ballot, we need to generate excitement and enthusiasm that drives a huge voter turnout. Bernie Sanders has demonstrated over the course of this primary that this campaign is able to do that — and that’s why Donald Trump is nervous.”

Sanders’ resurgence began late last year. After suffering a heart attack, and leaving many to wonder if he would be forced from the race, he received a major boost from liberal darling Alexandria Ocasio-Cortez.

A raft of polls out this weekend had Sanders leading or in second place in Iowa, vying with Biden for the top spot. The enthusiasm for Sanders was on display in Iowa on Sunday, when 1,100 people, according to his campaign, turned out to a rally in Sioux City co-hosted by Ocasio-Cortez and Michael Moore.