Joe Biden is heading into South Carolina’s Democratic presidential primary vote on Saturday as the heavy favourite to win, which would provide a much-needed boost just days ahead of the crucial Super Tuesday elections.

There was a point in the last few weeks when it seemed like the former vice-president’s South Carolina “firewall” might actually have some cracks in it. It seemed that the Vermont senator Bernie Sanders, Biden’s ideological polar opposite, might prevent him from winning the state decisively.

That moment came and went.

Now, Biden looks to be in the driver’s seat again in the first state in the deep south to cast its vote in the primary race, where African American voters form a majority of the electorate. In the 2016 presidential election, 24% of national Democratic primary voters were black.

“I’ve been confident about South Carolina because I’ve worked so hard over 30 or more years here … not to run for president, but to have the relationship with the community,” Biden told CNN on Friday morning. “I believe it’ll be the launching pad for me.”

Biden has campaigned on a message of dignity and unity, and stressed his experience as Barack Obama’s vice-president. He was the envy of other 2020 Democratic candidates this week, after he was endorsed by Jim Clyburn, the highest-ranking African American in Congress.

“Since Congressman Clyburn has endorsed the vice-president that has given him a great boost, a great energy. That has certainly provided clarity to individuals that were undecided,” said Clay Middleton, a South Carolina Democratic national committee member.

Joe Biden campaigns in Conway, South Carolina, on Thursday. Photograph: Jim Lo Scalzo/EPA

A day later, a new Monmouth University poll of South Carolina voters found Biden leading over Sanders by 20 percentage points. That poll was notably different from other recent South Carolina polls which showed Biden leading by single digits.

A solid win would give his campaign a shot in the arm days ahead of the Super Tuesday elections, when Democratic voters in 16 states and US territories will have their say on which presidential candidate they want to see take on Donald Trump in the November election.

Eight major Democratic candidates including Biden and Sanders remain in contention, and this week could mark a decisive make-or-break moment for several of them.

Biden entered the presidential race as the frontrunner and heavy favorite to win the Democratic nomination, but has since struggled to meet expectations. He placed a distant fourth in the Iowa Democratic caucuses, the first vote in the race in February. He didn’t do much better in New Hampshire.

But his campaign saw some improvement in the Nevada caucuses last week when he got about 18% of the vote, behind only Sanders, who is now considered the frontrunner.

Biden, a more moderate Democrat called out the progressive candidate directly at a campaign stop in McClellanville on Thursday, warning that Sanders’ Medicare for All proposal “will be a long, long expensive slog, cost over $35tn and the patients can’t afford to wait”.

Sanders’ signature policy Medicare for All, which would implement a government-run healthcare system in the US, is one of the most contentious policies being debated among Democrats this year, highlighting splits between progressives and moderates who largely favor an expansion of Obamacare.

Biden and his team have long argued that a win in South Carolina would rebuff his critics, and show he has the ability to attract a broad coalition of Democratic voters.

“The people know me. My entire career has been wrapped up in dealing with civil rights and civil liberties,” Biden said during the latest Democratic debate in Charleston. “I intend to win in South Carolina, and I will win the African American vote here in South Carolina.”

Mike McCauley, a veteran Democratic strategist based in South Carolina, said winning South Carolina could help Biden frame himself as the most prominent alternative to Sanders.

“For moderate Democrats like myself and my colleagues and peers across South Carolina we’re looking for who’s going to be the alternative to Bernie that’s going to emerge,” he said. “So I think that’s the springboard that South Carolina can give Biden is to provide that distance.”

While Sanders has risen to national frontrunner and become the candidate to beat, in South Carolina, where Biden leads in polling, the billionaire Democratic candidate Tom Steyer has also been a source of concern for the former vice-president.

Steyer has poured $20m into his campaign in the state and made a concerted effort to win African American voters. He has made a point of highlighting his positions on reparations and racial justice as he has campaigned throughout the state.

At a stop at a community resource center of North Charleston, Steyer said: “I really care about racial justice.”

“I think when I come to South Carolina and talk to African Americans they realize I’m not kidding,” Steyer told the Guardian. “I’m serious about it and I think as a result we share some goals and we share some history and I’m talking about things that they can believe in, because I’m serious about it.”

There is still a long way to go in the Democratic primary race before a presidential nominee is officially named at the party’s national convention in July.