BERNIE SANDERS is due on stage. But a stream of Bostonians—mostly hip, twenty-something, often lightly bearded—is still flowing into the waterfront convention centre, pressing politely forwards and flustering the similarly youthful volunteers who are organising the Vermont senator’s Democratic primary bid. When the doors are eventually closed, over 20,000 people are crammed inside, warming up to John Lennon and Hunter Hayes (“Baby, kids on the run/Gonna party like we just turned 21”) as they await the 74-year-old socialist and grandfather of seven. Thousands more are shut out, watching on giant screens: it is said to be the biggest primary rally in Massachusetts ever.

The insiders are exultant. They chatter, chant slogans and wave banners in joshing, undergraduate-accented praise of their hero: “Bern baby Bern”, “MIT feels the Bern”, “Bern4president”. When Mr Sanders stalks into view, all white hair, bony limbs and baggy suit, a glowering scarecrow-prophet, the roar is tremendous, the atmosphere hilarious. It is tempting to think the huge support he is drawing could be America’s biggest-ever student prank.

It is unexpected, admits Tad Devine, a veteran Democrat strategist who is working for him. When Mr Sanders declared his intention to stand in April, he says, “many people were incredulous. There was a feeling that there was no way this guy could knock such a formidable front-runner off the top spot.” Yet Hillary Clinton has been damaged by her peculiar use of a private e-mail server while secretary of state. And Mr Sanders, boosted by large, well-publicised rallies in student-heavy cities such as Portland, where he drew 28,000, and Seattle, where he drew 15,000, has soared.

Polls suggest he could win the first two Democratic ballots; he is running Mrs Clinton close in Iowa, which votes on February 1st, and has a handsome lead in New Hampshire. An average of national polls puts him on 25% and Mrs Clinton 42%. Joe Biden, the bereaved vice-president, who is still making up his mind whether to stand, is on 19%—a wedge of which, Mr Sanders’s aides believe, is an anti-Hillary vote that could come their way.

Pennies in a stream

The Democrats have been here before. In 2004 another left-winger from Vermont, Howard Dean, dazzled in the early campaigning, then died in the polls. Mr Sanders looks a bit different, however—not least because he is much more left-wing. The only socialist in Congress, he believes capitalism is screwing over 99% of Americans and, moreover, that the resultant “grotesque levels of income and wealth inequality” are no accident, but a scheme of the boss class to beggar the rest. “Why is it that with all the improvements to productivity from technology, people are being forced to work for longer hours, with lower wages?” he snarls on the stump.

To peg back the plutocrats, he would abolish the corporate funding of elections that he himself disdains. “I don’t represent the interests of the billionaire class and the corrupt men on Wall Street and I don’t want their money,” he says. He would nationalise health care, break up banks and swell the size of the state. He would provide free college education for all and convert outstanding student debt into soft loans, at an annual cost of $70 billion, paid for with a special tax on Wall Street. The crowd in Boston loved that.

No doubt, its members would have liked Mr Dean, too. Yet Mr Sanders’s recent progress suggests he may be drawing broader support than his predecessor. In some polls, he is outgunning Mrs Clinton against the leading Republican contenders, which suggests many Democrats are at least thinking through the consequences of him winning. A survey last month put him ahead of Mr Trump by five points and level with Jeb Bush. Those kinds of numbers attract money. Mr Sanders raised $25.5m in the three months to October, mostly in small contributions; the average was around $25. By comparison, Mrs Clinton raised $28m, much less than she had managed in the previous quarter. This puts Mr Sanders within reach of the $50m Mr Devine says he needs to be competitive through to Iowa and New Hampshire, where he already has nearly 100 paid staff. The southern states, where he is only starting to build his organisation, are a tougher prospect. Black Democrats in the South like Mrs Clinton and hardly know Mr Sanders. Yet his advisers trust that early success and the prevailing anti-establishment mood will awaken a storm of interest in him, obliterating these weaknesses. They predict that black voters will be wooed by his background in the civil-rights movement and that his emphasis on economic issues—which Mr Dean gave less time to—will win over blue-collar whites, including many formerly minded to vote Republican. The result, says Mr Devine, could be “early success leading to quick, decisive success thereafter”. If that is not entirely laughable, it is because Mr Sanders’s rise is being propelled by some novel factors. A combination of economic uncertainty and political polarisation has discredited the mainstream: the way Republicans are being bewitched by Donald Trump, another man selling simplistic solutions to complex problems, is further evidence of this. And Mrs Clinton’s slide, from shoo-in to damaged goods, has left some Democrats casting about for a back-up in an almost-empty field. “I’m looking for someone that excites me more than Hillary,” said Mara Klein Collins, a rare middle-aged attendee in Boston. Yet neither of these factors equates to a promise of electoral support.

The trouble with the millennials who dominate Mr Sanders’s rallies is that less than half of them actually vote. And there is still no reason to believe the wider support he is drawing will prove stickier than it was for Mr Dean. “The problems with candidates like that—and like me,” Mr Dean, who is backing Mrs Clinton, has said, “is that as you get closer to election time...you’re going to tend to want to see somebody who you think looks presidential.” That is, the joking stops there.

Those who argue that this time will be different perhaps misunderstand the role anti-establishment feeling is playing on the left. The anger Mr Trump is drawing on is primarily directed at the Republican establishment; by contrast, Democrats like their party leaders, and hate Republicans. That makes them likelier to revert to the primary candidate who looks most likely to win the presidential election—which, as even some of the enthusiasts in Boston ruefully conceded, will not be Mr Sanders.

His advisers understand this, which is why they are increasingly looking to turning blue-collar Republicans and the formerly apathetic—an effort in which Mr Sanders’s strong support from trade unionists is considered crucial. Over 70,000 union members have signed up to a support group, Labour for Bernie. In Larry Cohen, former leader of America’s largest communications union, Mr Sanders has also recruited a powerful ally. “The support we’re finding for him in working towns is overwhelming” said Mr Cohen, recently returned from an eight-city campaign tour.

Yet the unions have never been weaker; only about one in ten American workers belongs to one. That is partly a consequence of the deindustrialisation Mr Cohen laments, but also of a dwindling of the class-based loyalties and faith in collective action he shares with Mr Sanders. They also share a strong protectionist urge; yet, while most Americans recognise that globalisation has made the jobs market harder, over two-thirds want more of it. This is why, as a political movement, able to mobilise large sums of money and get its candidates elected, the hard left in American politics that Mr Sanders represents is almost dead. He is not about to revive it.