The former vice-president’s lead in the polls has proven durable, but some fear a replay of 2016

A small cheer went up as Joe Biden walked into the Detroit One Coney Island Restaurant, took off his sunglasses and beamed. The candidate shook hands and talked with diners for more than an hour while camera phones snapped.

The frontrunner for the Democratic nomination for US president in 2020 emerged from the restaurant to be greeted by cameras, reporters, onlookers and a young woman blowing a trumpet, accompanied by a man playing a cello.

“This is a marathon,” an upbeat Biden said. “We’ve passed the quarter mark and I’m feeling good.”

It was Thursday and the former vice-president had just emerged from the second Democratic primary debate bloodied but unbowed. His rivals had attempted to gang up on him like the assassins of Julius Caesar, twisting their knives on civil rights, the climate crisis, criminal justice, healthcare, immigration and women’s rights.

After it was over, no one claimed that Biden had destroyed his foes or offered Obama-like inspiration; the late-night TV comedian Stephen Colbert observed, “Democrats have gone from ‘Yes, we can!’ to ‘That’ll do’.”

But Biden had survived. Supporters took solace in his resilience, which is starting to look like a habit that could yet secure him the right to go up against Donald Trump in a fight for the White House. Already in this campaign, Biden has been confronted by women’s claims that he inappropriately touched them, been forced into a U-turn on government funding for abortions, faced allegations that he plagiarised sections of his climate crisis plan, earned opprobrium for his reminiscing about working with racial segregationists in the US Senate and been ambushed on his race record by Senator Kamala Harris in the first primary debate.

Yet, instead of collapsing, Biden retains a healthy lead in the opinion polls before next year’s caucuses and primaries in Iowa, New Hampshire and other states that will determine which Democrat goes head to head with Donald Trump in November 2020.

Two people whom Biden encountered at his campaign stop in Detroit on Thursday illustrated why, in his third bid for the White House, he is still the man to beat – but also the many pitfalls that lie ahead.

A key segment of his support is older voters, notably including African Americans. The Rev Wendell Anthony, president of the Detroit branch of the National Association for the Advancement of Colored People (NAACP), explained why.

“Because we know him,” said Anthony, 69. “And because he was with the first African American president and they have a record on healthcare, working with the community. He helped the city of Detroit in terms of the bussing, transportation, housing …

When you put his record up against some of the others, it stands a measure above and I just think that it’s not what you’re going to do, it’s what you’ve already done. He’s done enough to merit the kind of support that he’s getting.”

Facebook Twitter Pinterest Biden arrives at the restaurant. Photograph: Scott Olson/Getty Images

However, after Biden had embraced Anthony and climbed into his black limousine following the event, a woman rushed towards it shouting at him through the tinted window: “Three million deportations! Three million deportations! We don’t need your big answers. We need better candidates! Where is your apology?”

The incident highlighted how, by tethering himself to Obama as he promises to heal the nation’s soul, Biden has brought the 44th president’s own record under fresh scrutiny, as was evident at the debates. The Obama administration deported more than 3 million undocumented immigrants, far more than his predecessors George W Bush and Bill Clinton. Attitudes in the Democratic party have shifted since then – and threaten to leave Biden behind.

The anti-Biden protester was Brenda Valladares, 29, of Movimiento Cosecha, an immigrant-led movement campaigning for protection and respect. She said: “There are 3 million deportations that are on his hands that he was complicit with. I’m just reminding him because there’s still no answer. There’s still no apology for the atrocities that the undocumented communities experienced for eight years and that built and lay the groundwork for the atrocities and the hate that we’re experiencing today.”

Detecting such vulnerabilities, some of Biden’s competitors have offered bold ideas to fix the broken immigration system. Similarly, some have gone much further than Obama’s signature legislative achievement, the Affordable Care Act, with proposals for healthcare reform such as Medicare for All.

But others in the party fear this plays into Trump’s hands, fueling his argument that Democrats have become “radical socialists”, personified by the congresswoman Alexandria Ocasio-Cortez and her allies in “the Squad”. To this constituency, Biden seems like a safer choice.

In part this case rests on the notion that 2020 is no ordinary election. The Republican standard bearer is not a mainstream political figure such as John McCain or Mitt Romney but a celebrity businessman who has trashed norms, debased discourse and boasted about groping women. Therefore, the argument goes, this is not the time to experiment. Beating Trump is everything.

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Biden points to polls showing that he is well placed to win the crucial midwest battleground states that Hillary Clinton lost to Trump, restoring African American turnout to Obama-era levels and flipping blue-collar workers back into the Democratic column.

“I can win Michigan,” he said forcefully on Thursday. “They know me, I’ve worked my whole life. I come from the middle class. I understand it. I know what’s going on. I promise you, if I get the nomination, I will win Michigan, I promise you. I will win Pennsylvania. I will win Ohio.”

Facebook Twitter Pinterest Kamala Harris has taken Biden to task for his record on race. Photograph: Jim Watson/AFP/Getty Images

John Zogby, an author and pollster, said: “I always thought Biden is the one to go after Trump. He has the experience not to get bogged down in how low Trump can go. He’s the one who can say, ‘Donald, knock off this shit.’”

Others, however, are skeptical about whether the former senator can last the course in today’s Democratic party. Frank Luntz, a Republican consultant and pollster, said: “Biden is still clearly overwhelmingly the frontrunner but he is a frontrunner with some serious challenges ahead of him. He cannot afford a bad debate. He has to do at least mediocre in every debate between now and February.”

At 76, Biden would surpass Trump as the oldest person ever elected US president and would be yet another white man chosen from a historically diverse field that includes women, people of color and a 37-year-old mayor who is gay.

While he dominates the moderates’ lane, his most significant challenge may now come from the left. This week he was spared a direct clash with Senators Elizabeth Warren and Bernie Sanders, who appeared on night one of the two-part debate. Both are capable of firing up young supporters in a way that Biden might envy.

Luntz added: “I think that there’s a feeling within the Democratic party to go to the next generation. Medicare for All undermines Obamacare. The Green New Deal and the guaranteed living wage: that’s not Bill Clinton’s Democratic party and it’s not Barack Obama’s Democratic party.”

Many on the left fear that Biden v Trump would be a replay of 2016’s Clinton v Trump with a similar enthusiasm gap. They suggest that Biden’s candidacy is in a slow but inexorable decline. Neil Sroka, spokesman for the progressive group Democracy for America, who is based in Detroit and attended night one of the debate, said: “Joe Biden’s best day in the race was the very first one.

“He is the former vice-president of the United States who served with an extremely popular president, so it would be surprising if his candidacy imploded. It’s not a balloon that’s going to pop. It’s leaking air and there are moments when it leaks faster than others. Sometimes it gives the impression that it has stopped leaking altogether.”

Sroka, who worked on Obama’s first campaign in South Carolina, suggested that Biden could not take African American voters for granted.

“In 2007-08, black voters were Hillary Clinton’s base in that race all the way until Iowa. The most transformative day was Obama’s win in Iowa – suddenly we were inundated. I think it’s very likely Biden wins black voters right until the caucuses actually start happening. Just because someone has a lock on a constituency now doesn’t mean they will throughout,” he said.