The Scranton store where a young Joe Biden used to buy his candy is still in operation today, a stone’s throw from the wood-slatted house where the presidential candidate grew up.

It’s called Hank’s Hoagies now, in honor of the idiosyncratic Pennsylvania term for a sandwich on a long bread roll, and almost 70 years since Biden left Scranton, his presence lives on – in the form of a lifesize cardboard cut out lurking behind the store’s front door.

“We love him,” Tom Owens, the owner of Hanks, said by way of explanation. “He’s a great guy. I think he’d be a great president.”

Biden’s dream of becoming president had looked to be over at the end of February. The 77-year-old had lost, by some distance, the first three states of the Democratic primary, was running out of money, and had sagged badly in the polls.

Yet Biden won South Carolina, the fourth state to vote, on 6 March with a surprisingly strong showing. Even so, few predicted what came next.

Biden won 10 out of the next 14 states, on Super Tuesday picking up more delegates than anyone else. On the less super, but still delegate-heavy, Tuesday that followed, Biden won four out of six states and established a delegate lead that looks unassailable.

Speaking after his first big win, Biden seemed as surprised as anyone, and not just because an anti-dairy protester had rushed him on the stage.

Scranton, Pennsylvania: Biden’s hometown. Photograph: Mark Makela/Reuters

“They don’t call it Super Tuesday for nothing!” Biden told his supporters in Los Angeles.

“To those who’ve [been] knocked down, counted out, left behind, this is your campaign,” he said. “Just a few days ago the press and the pundits had declared the campaign dead.”

Biden wasn’t exaggerating. The influential, and frequently accurate, US polling site FiveThirtyEight had given Biden just a one in 12 chance of winning the nomination outright. Bernie Sanders was considered the most likely nominee – but not any more.

Media coverage has shifted from talk of a contested convention, where neither Biden nor Sanders have enough delegates to win the nomination, to whom Biden will pick as his running mate and what a Biden-Trump election will look like. Meanwhile, the ashes of Sanders’ campaign are being sifted through to work out what went wrong.

Super Tuesday not only handed back Biden the frontrunner status he held for much of 2019 – it handed him a big pot of money, too. His campaign said it had raked in $22m in the five days following that vote, a colossal amount considering it took Biden three months to raise $23.2m at the end of 2019.

Biden’s surge has little to do with Pennsylvania, which only votes on 28 April, and much more to do with his strong support among African Americans in the south. Nevertheless, Biden’s perceived earthy nature, which his Scranton childhood symbolizes, is a big selling point for voters hoping he could win back midwest states from Donald Trump in November.

“He’s an honest guy, the kind of guy you respect, which we seem to be lacking a little bit in our leadership now,” Owens said. “He’s down to earth. I think he’d be a great president.”

Biden is never shy of leaning into his Scranton background, having visited the city frequently while campaigning for Barack Obama, and Owens said Biden’s place of birth was visible in his persona.

“There’s a lot of blue collar people here. We talk a lot here. We know he has a tendency sometimes to maybe go on a little too much – that would be from living around here,” Owens said.

It is, in part, Biden’s talking that has been a major weakness. He turned in a series of lackluster debate performances through the end of 2019 and into 2020, sometimes stumbling over his words and at times looking like a relic of a bygone era.

In the past three weeks alone, Biden has mistakenly claimed: “Tomorrow is Super Thursday”, on the day before Super Tuesday; stated 125 million people had been shot dead in the US since 2007 – the actual figure is less than 500,000 – and launched into an expletive-laced row with an auto-worker about “AR-14” guns, when a years-long debate has actually taken place over the appropriateness of AR-15 weapons.

Donald Trump picked up on Biden’s gaffes when the president himself appeared in Scranton in the days after Super Tuesday. Appearing at the Scranton Cultural Center – on the street where Biden grew up – Trump didn’t hold back just because he was in Biden’s hometown.

Instead, Trump – who has faced much scrutiny over his own mental acuity – attacked Joe Biden’s cognitive abilities, listing Biden’s repeated gaffes and suggesting there is “something going on” with the former vice-president.

Biden didn’t respond to Trump, who wasn’t appearing in Pennsylvania by accident. Scranton, a town of 77,000 nestled in the rolling hills of north-eastern Pennsylvania’s Wyoming Valley, is firmly a part of America’s rust belt – a band of towns and cities stretching nearly a thousand miles from Wisconsin in the west all the way through Pennsylvania in the east.

The communities in the rust belt suffered more than most from de-industrialization, as coalmines, steel plants and car factories closed, and some areas still suffer from chronic unemployment. Scranton was once home to the coal industry, and the city and region boomed in the 1930s and 40s, but the decline was just as swift. As the US turned to oil and gas for its energy, mines closed and jobs were lost.

Biden and his family moved to Delaware in 1953 after his father struggled to find work in Pennsylvania. The future vice-president became a US senator for the state in 1973.

Joe Biden gets a hug from a supporter after he laid out his economic policy plan at the Scranton Cultural Center in Scranton, Pennsylvania. Photograph: Rick Loomis/Getty Images

Trump swept into communities like Scranton in 2016, wooing disenchanted working-class voters who had previously voted for Democrats with his hazy promise to Make America Great Again. He won Pennsylvania by 48.2% to Hillary Clinton’s 47.5%, and he narrowly triumphed in Michigan, Wisconsin and Ohio, too.

In 2020, that means Biden’s background is a key part of his case to be the Democratic nominee. If he is chosen, it could prove crucial in recapturing those states and the White House. Biden’s case for being the nominee is based, in part, around his ability to win in the midwest, and he will point to his convincing win in Michigan on Tuesday as supporting evidence.

That success in the rust belt was a long time in the making, and came after a concerted effort to make people aware of his upbringing: in the space of two weeks at the end of 2019 Biden was still pumping out shamelessly Scranton-specific advertisements, including “Scranton Values” and “A Kid from Scranton”.

In those ads, as in person, Biden looks good for his 77 years. Straight-backed and easily 6ft tall, he looks little different from the decade-old cardboard version of him at Hanks, which apparently is a popular gift.

“I have the same cardboard cut-out. I got it for my mom,” said Ailish Renton, who was buying a sandwich.

“She likes him. She also likes the way he looks,” Renton, 22, said of her mother. “She says he’s very handsome. And that she would kiss him.”

Unfortunately for Biden, few young people share Renton’s mother’s enthusiasm. Sanders won 61% of voters under 30 on Super Tuesday, compared with Biden’s 17%, and also handily beat Biden in the 30-44-year category. Last week, on less-super Tuesday, Sanders won more than 70% of voters under 30 in both Michigan and Missouri.

Ironically, given Biden’s experience is cited by his supporters as a positive that could help him navigate government, it is his longevity that frequently turns off young voters. During his years in the Senate Biden voted for the Iraq war and opposed bussing African American children to predominantly white, better performing, schools, and he supports moderate policies that are anathema to the 18-29 crowd.

On Wednesday Sanders said he was staying in the race, and his fervent youth support may be the only thing troubling Biden. Younger people, who already make up a relatively small slice of the electorate, are turning out in lower numbers than in 2016, when Sanders ran Hillary Clinton close, however, and it would take something unprecedented for Sanders to change that in the next few weeks.

If Biden can overcome his young people problem, and perhaps even if he can’t, then he will probably be the Democratic candidate for president. Win the election, and given his frequent visits to Scranton, it is likely the town will experience a visit by a president at some point.

Given his affinity with his hometown, however, it’s likely that even if Biden loses, he will always be welcome in Scranton.

Particularly by one young woman’s mother.