When the House majority whip, Jim Clyburn, endorsed Joe Biden ahead of the South Carolina primary it effectively set off a series of events that resulted in the former vice-president trouncing his rivals in the Super Tuesday primary contests on Tuesday night.

Before Clyburn’s endorsement, Biden’s lead in South Carolina had shrunk to single digits. It was an ominous sign for a candidate who underperformed in the first three Democratic primary contests and whose campaign stressed that South Carolina would serve as a firewall.

Biden’s ties to the African American community there, who make up the majority of Democratic voters, go back decades and the idea was that those relationships would carry him to victory in the state.

But then candidate Tom Steyer, a billionaire, was making an aggressive play to win over black voters in South Carolina. And Bernie Sanders’ aggressive campaign and grassroots supporters in the state were helping the Vermont senator make gains.

With just days to go before the 29 February primary, Clyburn hadn’t endorsed anyone and every candidate wanted it. He is the highest-ranking African American Democrat in Congress and an influential figure in his home state of South Carolina.

Clyburn, before his eventual endorsement, conceded that Biden’s rivals were gaining ground.

“These things usually tighten up when you get close to an election. So, we don’t know. We will find out in about 10 days,” Clyburn said in an interview with CNN.

Then came the endorsement.

“You cannot overstate the impact of Clyburn on South Carolina Democratic politics,” said Isaac Wright, a Democratic strategist and partner at the Forward Solution Strategy Group.

To be sure, Biden’s recent success was not singly due to one endorsement. He had always polled ahead of the rest of the field in South Carolina and he had been methodically picking up endorsements there. But Clyburn’s public backing helped cement Biden’s legitimacy among the Democratic electorate in the 2020 primary.

Following Biden’s decisive victory in South Carolina on Saturday, his main moderate rivals within the primary, the former South Bend mayor Pete Buttigieg and the Minnesota senator Amy Klobuchar, quickly dropped out of the race and endorsed him. Other endorsements, including the coveted backing of former Senate Democratic leader Harry Reid, Barack Obama’s US ambassador to the UN Susan Rice and former candidate Beto O’Rourke, flooded in for Biden.

“That substantive victory in South Carolina is what set off a chain reaction in the next few days – the Buttigieg endorsement, the Klobuchar endorsement and what amounts to all but a clean sweep on Super Tuesday,” Wright added.

The endorsement came just a few days before the election but Biden’s poll numbers had begun to tick up dramatically and he won the state by about 30 percentage points.

“Black voters turned out and they had their voices heard and they are on the trajectory of propelling Joe Biden to be the Democratic nominee. Clyburn’s endorsement was part of a flood of good fortune for Biden,” said Eric Goldman, a Democratic consultant.

Goldman noted though that Clyburn’s endorsement was just one part of the turnaround. Goldman stressed Biden’s “longstanding” ties to the African American community.

That victory seems to have set off a domino effect of support among Democratic voters in southern states and minorities. In the 14 primary contests on Tuesday, Biden won every southern state. According to exit polling Biden’s victories in some of these key states were largely thanks to strong support among minority voters.

And on Wednesday, Biden’s remaining moderate rival in the primary, the former New York mayor Michael Bloomberg, dropped out and endorsed him.

The Super Tuesday victories for Biden also elevated him back into frontrunner status. He came away from Super Tuesday with more delegates than Sanders and the Massachusetts senator Elizabeth Warren.

Biden’s turnaround, from a campaign on life support with no victories and dwindling cash to frontrunner, had happened in an eight-day period, with Clyburn’s endorsement marking the beginning of the dramatic change.

A day after Super Tuesday Clyburn, again speaking on CNN, admitted he was surprised with the extent of Biden’s victories the night before.

“I was a bit surprised: it did go better than many of us expected,” he said.