Branko Marcetic had doubts about writing a Joe Biden book. Marcetic, a staff writer for the left-wing magazine Jacobin, initially dismissed a friend’s suggestion out of fears the former vice president wouldn’t go the distance. And yet he dove into the project last May as Biden was a frontrunner—and kept at the project as the candidate stumbled in the polls. “The whole thing was a rollercoaster,” Marcetic told me. By the time “Yesterday’s Man: The Case Against Joe Biden” arrived on doorsteps earlier this year, the author’s initial misgivings appeared justified: Biden’s campaign had collapsed. Now weeks later, Biden has been resurrected and the book is relevant for progressives trying to fend off a rejuvenated party establishment. “It’s been very strange,“ Marcetic said. “God knows what’s going to happen next.”

Biden’s revival in South Carolina, and surge on Super Tuesday, shocked the pundits as the once-floundering candidate leapfrogged Bernie Sanders in the race. With decisive victories over the coming eight days in states such as Florida, he could take a delegate lead to the Democratic convention. Marcetic’s skepticism about the book reflected a broader view within the pro-Bernie media ecosystem: Why make a case against Biden when he seems to be doing it himself with slip-ups on the campaign trail and debate stage? But the assumption among many Sanders loyalists that Biden would fade away has been supplanted by a sense of urgency to stop him. They’re not only questioning Biden’s record, like voting for the Iraq war, but also his fitness for office. “We’re about to walk off a cliff if we let Joe Biden be the nominee,” said Cenk Uygur, host of the progressive YouTube program “The Young Turks.”

The anti-Biden pile-up may be the last stand for Bernieworld, a final social media assault before the primary—and the possibility of a President Sanders, a dream of many on the left for nearly five years—becomes out of reach. The amplification of questions about Biden’s fitness for office has demonstrated the reach of the pro-Bernie media world, with widely followed lefty journalists and podcast hosts sharing clips and claims to millions. It may not be officially coordinated, but it doesn't have to be to be effective. The Sanders movement doesn't have one brain, necessarily; social media allows its intelligence to be distributed. But the campaign also highlights the limits of an alternative media apparatus, given that mainstream newsrooms are less likely to casually throw around medical diagnoses from afar. A Biden adviser dismissed such commentary on the left as an act of desperation from Sanders supporters. “Bernie’s campaign lost 10 of 14 Super Tuesday states, got crushed in the suburbs, crushed with African American voters and had their whole theory of his revolution shot down by voters turning out in record numbers to vote for Biden,” the adviser told me. “He’s behind in the delegate count. Desperate times call for desperate measures, I guess. Disappointing that they would turn to this trash.”

The Sanders campaign, officially, isn’t similarly challenging Biden’s cognitive abilities, but has suggested that the 77-year-old candidate doesn’t have the stamina of their 78-year-old. Over the weekend, Sanders campaign manager Faiz Shakir drew attention to Biden spending comparatively less time speaking on stage than Sanders. The Sanders campaign also pushed back against the idea of the two leading candidates sitting during the next debate, on Sunday in Phoenix, Arizona. “Why does Joe Biden not want to stand toe-to-toe with Sen. Sanders on the debate stage?” senior adviser Jeff Weaver asked, per Politico. A Biden representative told Politico they’d participate in whatever format the Democratic National Convention and CNN decide upon, whether “standing, sitting, at podiums, or in a town hall.”