The former vice-president staged a comeback as Democrats fear a repeat of the 2016 struggle between Sanders and Clinton

Joe Biden has staged one of the greatest comebacks in modern political history to become the front runner of the Democratic presidential race after winning a majority of the crucial Super Tuesday primary elections.

A week ago the former vice-president, who first ran for the White House in 1988, had never finished first in a state primary or caucus. Now he has won 10 and is the favourite to clinch the Democratic nomination, setting up a battle with Donald Trump in November’s US election.

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“People are talking about a revolution. We started a movement,” Biden said in his victory speech in Los Angeles on Tuesday night, knocking one of his rival Bernie Sanders’ signature lines.

The path forward, however, remains rocky and uneven, with Sanders determined to fight to the bitter end. Democrats fear a replay of the bruising struggle between the Vermont senator and Hillary Clinton in the 2016 election.

But for now, Biden, 77, has the most important political superpower: momentum (or “Joementum”, as his campaign calls it). After setbacks in Iowa, New Hampshire and Nevada left him looking out of sorts and out of cash, Biden bounced back last Saturday by winning South Carolina by nearly 30 percentage points, including 61% of the black vote.

In a stroke, he had won the electability argument. Moderate rivals quit the race and consolidated behind him. Biden’s performance on Super Tuesday, when a third of Democratic delegates are decided, then surpassed even the most optimistic predictions. He swept at least nine states, from Massachusetts in the north to Alabama in the south to the major prize of Texas, where Latino voters had been expected to tip the balance in Sanders’ favour.

As a political miracle, it earned comparisons with Harry Truman’s election win in 1948 (“Dewey Defeats Truman,” said an infamously preemptive newspaper headline) and Bill Clinton’s “comeback kid” moment in 1992. “I’m here to report: we are very much alive!” the revivified Biden declared at a rally in Los Angeles, promising: “This campaign will send Donald Trump packing.”

It was a victory built on two pillars: the Democratic establishment unifying against the leftwing Sanders and support from nearly two-thirds of African American voters in the south. Biden also benefited from suburban moderates who have been politically galvanised since Trump’s election and helped win the House of Representatives for Democrats in 2018.

With the billionaire Mike Bloomberg withdrawing and endorsing Biden on Wednesday, the nomination is now his to lose. And with states such as Arizona, Florida, Georgia, Mississippi and Ohio voting later in March as the primary race continues, the calendar works in his favour.

Bill Galston, a former policy adviser to Clinton, said: “Nothing succeeds like success. The scholars who’ve been talking about momentum being more important than organisation have got a new, very substantial piece of evidence on their side.

“My best guess is Mr Biden will end the month with the most delegates. If this turns out to be a war of attrition, he can win it.”

But four years ago Clinton emerged from Super Tuesday with a delegate lead of more than 200 and still became mired in three months of trench warfare; Biden’s lead will probably be closer to 60. And Sanders is nothing if not tenacious. On Tuesday he won California, Colorado, Utah and his home state of Vermont, where he used a rally to draw sharp distinctions between himself and Biden.

Facebook Twitter Pinterest Supporters of Bernie Sanders cheer during a Super Tuesday election rally in Essex Junction, Vermont, on 3 March. Photograph: Matt Rourke/AP

“You cannot beat Trump with the same old, same old kind of politics,” the 78-year-old democratic socialist declared, listing past policy differences with Biden on social security, trade and the Iraq war. “This will become a contrast in ideas.”

On Wednesday, he launched three new TV adverts. And he may yet get a boost from the Massachusetts senator Elizabeth Warren, the third and last major candidate in the race, if she drops out and endorses him.

Biden’s candidacy has always faced the challenge of how to present him as a positive, motivating force, not merely a receptacle for anti-Sanders and anti-Trump sentiments. He has begun to reassemble Clinton’s 2016 coalition but is not there yet: her numbers among African American voters were higher, while Sanders leads among Latinos, younger voters and a fiercely loyal progressive base for whom Biden represents the past, not the future.

But Galston, a senior fellow at the Brookings Institution thinktank in Washington, said: “Biden has found his voice. He is making the most realistic appeal to improving the lives of the American people. He can restore the standing of the United States in the world. He can restore honesty and dignity to the Oval Office. He can begin to heal the nation. It’s not a complicated message.”

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In practical terms, how Biden should convey this message is less clear. Super Tuesday upended many assumptions. Biden had performed poorly in 10 televised debates yet appeared to pay no price. He picked up five states where he did not even campaign. In Virginia, Biden spent less than $200,000 compared to Bloomberg’s $12m, yet Biden won it by more than 25 percentage points.

Now the frontrunner, Biden’s liabilities will come under renewed scrutiny. His long political career includes support for a 1994 crime law that critics say contributed to mass incarceration. Several women have in the past accused him of inappropriate physical contact. The Trump impeachment saga raised doubts in some minds about Biden’s son Hunter’s business dealings in Ukraine, though there was no evidence of wrongdoing. He makes regular gaffes that Republicans and comedians ensure will go viral.

Biden’s ability to generate high turnout may set off alarm bells in Trump campaign headquarters. But the US president will relish the prospect of a long, acrimonious battle between Biden and Sanders that could go all the way to a contested convention in July. The former vice-president’s biggest challenge may not be so much winning the nomination as unifying a restive party.