American politics has a new comeback kid.

That was what Bill Clinton called himself after reviving his presidential campaign in 1992. Now, even more improbably, Joe Biden – who, at 77, is the youngest man in the race for the Democratic nomination – has risen like Lazarus to win nine states on Super Tuesday and become the frontrunner.

“We are very much alive!” he told rejoicing supporters in Los Angeles.

It was one of the stunning reversals in recent political history. Less than a month ago Biden slunk away from New Hampshire with his tail between his legs even before the votes were counted. When he trailed in fifth, political obituaries were written. Bob Shrum, a Democratic strategist, told the Guardian: “For him to recover from this would be a political miracle unlike anything we’ve seen in modern presidential politics.”

The conventional wisdom was that Super Tuesday – when a third of Democratic primary delegates (who eventually nominate the candidate at the party’s national convention in July) are decided – would not be a question of can the Vermont senator Bernie Sanders win, but how big will his lead be.

But last week, everything changed. It started with James Clyburn, who is African American and became a member of the House of Representatives in 1993. Attending his accountant’s funeral, Clyburn was stopped by an older woman near the front of the church. “Young man, I want you to whisper in my ear who you are voting for,” she told him.

At that moment, Clyburn, 79, effectively the dean of South Carolina politics, felt he had to make a public endorsement. He did so for Biden in an emotional speech, handing Barack Obama’s vice-president a massive boost. Biden won the state’s primary vote on Saturday by nearly 30 percentage points, including 61% of the black vote, vindicating all the talk of Biden’s South Carolina firewall. He was back off the ropes.

It was the pivotal moment because it established Biden’s credibility, electability and viability for the moderate wing of the party. It was clear that he – not the billionaire former New York mayor Mike Bloomberg, the former South Bend mayor Pete Buttigieg or the Minnesota senator Amy Klobuchar – stood the best chance of defeating first Bernie Sanders, then Donald Trump in November’s election.

Facebook Twitter Pinterest Supporters attend a rally for Joe Biden in Los Angeles, California. Photograph: Kyle Grillot/Reuters

It was time for moderates to get in line, especially after Sanders’s comments in a TV interview – acknowledging Cuba’s literacy programme, “Is that a bad thing, even if Fidel Castro did it?” – crystallised their fear of an electoral car crash. Buttigieg remarked: “I don’t want as a Democrat to be explaining why our nominee is encouraging people to look on the bright side of the Castro regime when we are going into the election of our lives.”

On Monday Buttigieg and Klobuchar duly quit the race and endorsed Biden, avoiding the fatal error of Republicans who failed to unite against Donald Trump in 2016. The former presidential candidate Beto O’Rourke, the ex-senator Harry Reid and the former national security adviser Susan Rice did so too. Suddenly, Super Tuesday would pit Sanders against the centrist Avengers.

“Yes, the moderates are consolidating,” said comedian Stephen Colbert. “We are reaching extreme levels of centrism.”

Super Tuesday: five key takeaways as two frontrunners emerge Read more

South Carolina proved a blueprint, not an outlier, as Biden looked on course to win the most delegates on Super Tuesday. African Americans in the south, moderates and suburbanites supported him in droves. Counter-intuitively, it was his coalition that boosted turnout, whereas so far in 2020, Sanders has failed to expand his base. A massive surge in Virginia worked in Biden’s favour, a clue as to why Trump has long been wary of him.

Moe Vela, a board director at TransparentBusiness and a former senior adviser to Biden at the White House, said: “It is an incredible night for Joe Biden. We’re seeing a very clear pattern that Democrats across the country, across racial lines, across gender lines, are loudly saying that socialism is not for them and it’s not a revolution they seek.”

He added: “Joe Biden brings predictability and security and stability and represents a course correction. People don’t want a radical extreme. They want to wake up and feel good about the country again.”

Tuesday’s results also proved Hollywood screenwriter William Goldman’s maxim that “nobody knows anything”. Democrats have held 10 televised presidential debates, with Buttigieg, the California senator Kamala Harris, Klobuchar and Massachusetts senator Elizabeth Warren notching wins and Biden performing terribly. But in the end, all that talking and sparring counted for nothing. There were five states where Biden did not campaign, and where Sanders and Bloomberg built big operations, yet which Biden still won.

Facebook Twitter Pinterest Sanders has galvanized young people hungry for change but struggled to win over older voters in the suburbs. Photograph: Caitlin Ochs/Reuters

Momentum, or “Joementum” as his campaign calls it, beat money. It is, once again, a humbling reminder that most voters are not tuned into every debate or every twist and turn of Twitter. Go to any Trump rally and ask about the latest Washington scandal and you will often be met by blank stares or so-what? shrugs.

But Super Tuesday has been clarifying in two other ways: one uplifting, one sad. First, money can’t buy you the presidency: Bloomberg had splashed out half a billion dollars and got hammered. Second, the glass ceiling has been reinforced and America will again not elect a female president: Elizabeth Warren could not even win her home state of Massachusetts. Both will face renewed pressure to withdraw.

So what began as the biggest, most diverse field in history is now a two-person race that looks a lot like 2016: a moderate establishment Democrat representing a third term of Obama versus the leftwing populist Sanders. It should come as no surprise that voting patterns are broadly similar, with Sanders galvanising young people hungry for change but struggling to win over older voters in the suburbs.

Hillary Clinton ran up the score on Super Tuesday in 2016 yet the primary dragged on, bitterly and divisively, and she eventually lost to Trump. With Sanders taking California, Colorado and Vermont on Tuesday, there is an even greater chance of a long drawn out fight this time, possibly ending in a contested convention. And even if Biden prevails, his age and gaffes could prove a liability.

The original comeback kid, Bill Clinton, was 45 at the time of his resurgence in the New Hampshire primary, a fresh face like Jimmy Carter before him and Barack Obama after him. Clinton is now 73 – which still makes him four years younger than Biden.