Let us start with the crowds, for they are at the heart of Jeremy Corbyn’s story. They queued around the block in 2015 to see him claim the Labour leadership; weeks after he last ran to be prime minister they gathered in a field in Glastonbury and sang his name.

And in 2019 he can still pull a crowd. They’ll come miles, pack out halls, end up so far back that they can’t hear, let alone see him. All for a politician not known for his soaring oratory; whose CV boasts not one single day in government.

But they come anyway – to hear a contender for power promise a more generous public sector, a government that cares, a different politics and language than they’ve known for decades. An era that could begin next week.

A Saturday afternoon at the community hall in the West Yorkshire village of Mytholmroyd is typical. Tickets for the Labour leader’s pitstop went on offer one evening at teatime; they’d all gone before breakfast next morning. Now there’s about 300 people in their mud-caked walking boots and waterproofs.

Calder Valley is the sort of seat Corbyn must win to get into No 10 and, as he reminds activists on the penultimate weekend of the campaign, it’s there for the taking. Tory MP Craig Whittaker holds it by a tiny majority of just 609 and the Greens, who racked up 631 votes in 2017, are sitting this one out.

Party staffers call this event a “Me-Mo”, a member mobilisation, yet Corbyn avoids any hard sell. No one is asked to do anything for him. Rhetorically, he stands in for the audience, while they stand in for the country. No “I”, no ”you”, just ”we”: “When we win, the nurse wins, the teacher wins, the doctor wins.” No sooner does he end then there’s a surge of people wanting a word, a handshake, a selfie. His exit from the hall can be measured in quarter-inches.

A boy shouts, “Change the world!” and the 70-year-old beckons him over, so the suited entourage halts again. Brown-haired and beaming, Solomon is 12, “but my teachers say I’m going on 40”. His number one issue is the threat of climate breakdown.

Facebook Twitter Pinterest Jeremy Corbyn talks to supporters at Mytholmroyd Community Centre. Photograph: Christopher Furlong/Getty Images

“If Boris gets in, I don’t know what my future or the planet’s future even looks like.” This is a family day out, with his parents driving up from Holmfirth. They’ve been canvassing for Labour and dad Moses admits some of the conversations on the doorstep are tough, especially once the subject is Corbyn. He’s heard it all: weak leadership, Brexit, but most of all anti-semitism. “It’s the media, isn’t it?” he says, and shoots me the kind of look Solomon’s teachers save for the naughty boys.

Local Labour councillor, Steve Sweeney, breaks into a grin as wide as the River Calder as he remembers organising a meeting for the Labour leader at Hebden Bridge in May 2017. Over a thousand came to that one rally, so impossibly many that Corbyn had to go outside to deliver his speech a second time. Some latecomers wanted in so badly they stood in the river. “I can’t imagine they caught a word.”

“Perhaps no historical phenomenon has been so thoroughly neglected by historians as the crowd,” wrote French scholar George Rude in his classic The Crowd In History. Whether at Bastille in 1789 or Peterloo in 1819, the “faces in the crowd” were considered not as a “living and many-sided phenomenon” but “an abstract formula”. The activists who thronged in driving rain at Sheffield last month to cheer Corbyn as he went on Question Time: Leaders Special were not doing anything half so dramatic, but they and others have been deluged in condescension.

To much of the press, they are little more than “Corbynistas”, bovine hordes lowing against the ideologically impure. Yet those grassroots supporters have called the past half-decade better than most in the Westminster village. As insiders laughed at his leadership chances, it was the growing crowds that showed he was a serious contender. When Labour MPs demanded Corbyn quit, his biggest support came from the crowds mobilising outside parliament.

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Against press onslaught, Corbyn’s supporters have been his defence. When the polls look poor, his crowds have served as a reminder that anything is possible. For Corbyn himself, they show that he heads a “social movement”. Over the last few hours of this historic election, their role will be vital. And if Labour lose badly on Thursday night, then one big question on Friday morning will be who and what Corbyn’s crowds will accept.

One thing is clear: they are not to be taken for granted. The crowds this campaign would delight any other politician but by Corbyn’s standard they are typically smaller and older. Cold, wet evenings are no friend to the outdoor epic meeting, and the Labour leader is no longer the promising up-and-comer he appeared to be at Glastonbury two years ago. Yet senior advisers still puzzle over why his dire personal ratings have not enjoyed anything like the boost they got in 2017.

And for much of this year, some Corbyn-supporting MPs have been privately worrying about something else: dimming enthusiasm among the base, disappointed over his wavering on Brexit and the leadership’s foot-dragging over its anti-semitism crisis, which has been allowed to fester and grow into one of the defining issues of this election.

The Guardian’s own evidence backs this up. For this piece, analysts from our data and insight team studied website traffic since the start of 2017, and found that readership for Corbyn-related headlines had tailed off since this spring, sliding below that of all pieces on UK politics. On one of the leading liberal-left news sites in the English-speaking world, the British politician who draws most readers is Tory Boris Johnson. His novelty as prime minister, as well as his wrangling over Brexit are surely two big reasons why, but it also looks as if the thrill is not gone, but may be going.

Facebook Twitter Pinterest Corbyn prepares for an interview with Sky News at the community hall in Mytholmroyd. Photograph: Sean Smith/The Guardian

In Mytholmroyd, Labour councillor Roisin Cavanagh has spotted something else to worry her leader. After a decade of austerity, the hard-up voters she canvasses “have lost the ability to believe that things can be different”. She recently met a woman who had lost her home thanks to the bedroom tax and now lived in a small flat. With no room to put up her daughter, she complained of feeling isolated. Asked what she made of the bedroom tax, the woman said simply: “It’s the system, isn’t it? That’s what it does to people like me.”

On the other side of the same community hall, Sky News are setting up to interview the Labour leader. Armed with three cameras, the crew strive to make a room normally used for the Stay and Play toddler group into a setting fit for a would-be prime minister. The interview with Sophy Ridge goes out next morning, two days after the London Bridge terrorist murders and just before Corbyn gives his key foreign policy speech of the campaign.

While the presenter pores over her notes, a set of drawers is rolled out of shot and swapped for a Christmas tree. The camera operators stare down their viewfinders with no sign of festive cheer. They inch the tree back and forth, before glumly agreeing to stick with the drawers. In five minutes, navy-suited Corbyn, his wife Laura Alvarez, his chief strategist Seumas Milne and other members of his entourage will enter and the cameras will roll.

This is what election campaigns demand of party leaders: to sweep from one artfully-composed room to another, precision-delivering messages as they go. Except Corbyn doesn’t do slick.

Faced with an audience, the Labour leader can be engaging, but on the typical studio ping-pong he is prone to sulk. This trip to Yorkshire follows easily his worst week of the campaign: a front page attack from the chief rabbi for allowing “a new poison” of anti-Jewish racism to enter the party, followed by such a spectacular mauling from the BBC’s in-house pit bull Andrew Neil that Johnson will not be dragged in front of him. A major controversy in this election is whether, as Labour allege, the national broadcaster is failing to hold his opponents to account.

“It hurts because he is my husband and I don’t like seeing him treated this way,” says Alvarez, in rust cardigan and red scarf. “But really we should all be asking: What is happening to our democracy?”

Facebook Twitter Pinterest Jeremy Corbyn speaks to supporters before taking part in the Channel 4 climate debate. Photograph: Sean Smith/The Guardian

A few days beforehand, I went to Channel 4 in London to watch Corbyn debate other leaders on climate change. It could have been a good night. Johnson had ducked out again, to be replaced with a giant ice sculpture, while the other leaders all had weak-spots. Yet the youngish activists watching in the Channel 4 spin room went from receptive to restive.

When Corbyn showed his commitment to forestry by waving his own hard-copy dead-tree report, some moaned. To underline his green credentials, he boasted how rarely he stuck on the central heating, adding, “I’m quite miserable, actually”, prompting well-wisher Matthew Butcher to mutter: “Oh, mate – I did climate comms and the first thing they teach you is never say it’s miserable.”

The biggest bafflement was summed up by another Labour-supporting environmentalist: “He was stood next to a giant fucking melting ice cube – how could he not once turn to it and say, ‘What does Boris Johnson think? Let’s ask him.’ An easy goal but he didn’t tap it in.”

That lack of attack runs through Labour’s election, from its mushy slogan of “Real change is coming” to whether it is about the NHS or a “transformative government”, to the confusion over who calls the shots. Some say John McDonnell, formally Labour campaign chair, runs things; others swear it is Corbyn’s former chief of staff Karie Murphy, officially election campaign chief. This Thursday, Labour’s John Healey appeared on Radio 4’s Today programme to pledge an end to rough sleeping – a “moral mission” that deserved big billing yet was overshadowed by a commitment from his colleague Angela Rayner to give free breakfasts to all primary pupils.

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On some mornings, it has felt less a campaign to form the next government and more like an advent calendar. “It really is ‘vote Labour and get a free microwave’”, says one frontbencher and Corbyn loyalist, recalling the fat raspberry blown by an adviser to Barack Obama at Ed Miliband’s 2015 campaign.

One of New Labour’s signal moments was Gordon Brown’s decision in 2002 to raise National Insurance by a penny and invest in the NHS. Paving the way for that one policy took No 11 well over a year of work. It lured a starch-shirted banker, the now-late Derek Wanless, to chair an independent report that as if by magic reached exactly the conclusion the chancellor desired.

In today’s money that programme cost £64bn. By comparison, a fortnight ago shadow chancellor McDonnell said he would spend nearly £60bn to compensate women “robbed” of their pensions. Whatever the merits of that policy, Labour made no attempt beforehand to lay the ground for it and gave little reassurance afterwards on how it could be afforded. In a country that prints its own currency and with borrowing rates near zero, it is affordable; but it is also as if such electoral niceties are beneath them.

Two forces are at play here. The first is what Corbyn’s policy chief Andrew Fisher dubbed in his resignation letter this September a “lack of professionalism”. The second is a belief held across the new left that the banking crash of 2008-9 effectively crushed the old common sense about how an economy should run, how politicians should look and what they must say. Corbyn’s critics often conflate these distinct forces; the difficulty of his supporters is to avoid the first.

“Common sense is not something rigid and stationary,” wrote the communist Antonio Gramsci, even as his native Italy collapsed into fascism. “[It] creates the folklore of the future, a relatively rigidified phase of popular knowledge in a given time and place.” The struggle, he believed, was to replace it with “good sense”.

Facebook Twitter Pinterest Jeremy Corbyn backstage with shadow cabinet members at a rally at Leeds Beckett University. Photograph: Sean Smith/The Guardian

To see how that struggle plays out now, look at how Labour and even the Conservatives have shifted since the crash. Kevin Farnsworth, a senior social scientist at the University of York, has fed the two main party manifestos for every election since 1945 through software that assesses similarities and differences between them based on their key concepts and phrases. The manifesto on which Brown lost the 2010 election was far closer in its language and preoccupations to the Tories of that year than to Corbyn’s platform in 2019. Also vast is the conceptual distance between Ed Miliband’s offering in 2015 and the one that followed just two years later, which Farnsworth describes as “the radical break”.

It’s Saturday evening, Corbyn’s last public outing is an NHS rally at Leeds Beckett student union, a venue more used to indie bands and messy discos. The queue outside winds around and around the pavement, while inside Amanda Burns sips at a glass and waits for tonight’s act. Getting others to support Labour is proving far harder than last time, she says, “especially among lefties. It’s like they’ve got Stockholm syndrome and think their prisoner [Johnson] is their master”.

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An artist, Burns used to teach at a city school, until it converted to an academy and axed most of the creative arts department. Her “gig buddy” and former MA teacher Rebekka Kill bobs over. Once involved with the Anti-Nazi League, she went off politics for decades – until in 2015 she spotted Corbyn. “It’s his integrity. His honesty was just different from what we’d been served up.” Yet ask these activists which way they’ll jump if he goes soon and they expertly reel off the contenders. Rebecca Long-Bailey: nice-seeming, but quiet. Keir Starmer: a “centrist suit”. Jess Philips: someone nearby makes a vomit noise.

Up the backstairs in the dressing room, wedged underneath a rail of coathangers are Corbyn, and his frontbenchers Richard Burgon and Angela Rayner. They sit on some leatherette sofas in a dark brown that must hide an epic history of spills. How do they think this election differs from the last? Corbyn kicks off: “Despite the predictions, it’s not been a one-issue campaign, but an election along many dimensions. That was largely our doing.”

But on that one issue of Brexit, how do the Labour leave areas they’re blitzing in these last few days respond? Rayner admits that in her patch of Ashton-under-Lyne voters are “more despondent than in 2017. They wanted one thing done and it’s not happened – and they hate us all”.

Despite having done about three set-pieces a day every day all over the country for the past four weeks, Corbyn shows no strain, not even a cold. He runs regularly, say advisers, and goes to the gym. A few days back, he was at the Sobell leisure centre near Arsenal’s stadium, when a man flew out of the showers “completely naked,” laughs the Labour leader, who was torn between squeamishness and a politician’s civility. “I was like, ‘please put it away, get a towel’ but he was: ‘I want to talk to you about my nan’s housing.’”

Facebook Twitter Pinterest Jeremy Corbyn addresses a crowd of supporters next to a statue of Robin Hood in Nottingham. Photograph: Joe Giddens/PA

Amid all this, he finds out that Burgon turns 40 next September. “Well, that’s the agenda for next year’s party conference sorted,” says Corbyn, “but will a mere five days of celebration be enough?” It is a long way from the humourless grandpa image: “My dears, my friends, let’s go and inspire the waiting masses.”

On that front, it is health spokesman Jon Ashworth who wins. He recalls how the NHS was described by its creator Nye Bevan as “a piece of real socialism” and goes on to argue that the new universalist pledges in the manifesto – for broadband, for housing, for rail – are straight out of Labour tradition. “When people ask how you can afford it,” he bellows, addressing one big question on the doorstep, “ask them how amid the rubble and carnage of the second world war did we build an NHS?” The evening ends with the crowd chanting the anthem of Labour in 2019 – not the Red Flag but “Oh, Jeremy Corbyn”.

The evening charges up not just the members but the frontbenchers, judging by their buzz in an Italian restaurant afterwards. Alvarez shows pictures of the household cat, El Gato, and frets that for all his slimline good looks he is a Tory, “a selfish individualist”.

In her spotted brothel-creepers, Rayner, the self-described “council estate kid”, ribs Milne endlessly about his moneyed background. Over risotto, Corbyn takes a break from worrying about how to get Islington council to bring more services back in-house, to show quite detailed knowledge of how car thieves used to jam a lock, expertise gleaned from when some local youths helped him break into his own car. As the evening breaks up and he prepares for tomorrow’s speeches, he asks if we enjoyed the rally: “Lovely atmosphere, wasn’t it?”