It is the first primary in the US Deep South, and while bigger trophies are just over the horizon on Super Tuesday, Saturday's vote in South Carolina has the potential to dramatically shift the conventional wisdom about the race for the Democratic presidential nomination.

South Carolinians head to the polls for a Democratic primary being billed as the first real test of which candidate is favoured by African-American voters. If polls are any indication, the race is Joe Biden's to lose.

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The former vice president has run for president three times during his 48-year career in politics and has yet to win a primary or caucus. In the three votes so far this year, he has come in fourth, fifth and second. He needs a win in South Carolina and is counting on his ties to former President Barack Obama to help deliver it.

Polls out of the state released during the week showed Biden with a commanding double-digit lead over Sanders, and an even greater advantage - 45 percent to 13 percent - over current frontrunner Bernie Sanders among likely black voters.

A poor showing by Sanders in South Carolina runs the risk of dimming the aura of invincibility that has surrounded him since his blowout win in the Nevada caucuses. The unlikely event of a Sanders win, on the other hand, would mean an all-but-certain end to the Biden candidacy and clear the path ahead for the independent senator from Vermont.

For candidates not named Sanders or Biden, South Carolina is about keeping momentum headed into the Super Tuesday primaries on March 3, when 14 states and American Samoa hold their primaries and about a third of the pledged delegates needed to secure the nomination are up for grabs.

"What happens in South Carolina does matter, mostly because of what the coverage is going to be over the three days leading up to Super Tuesday. If someone seems out of the running, they're going to lose value," said Achim Bergmann, a Democratic strategist whose firm works in a number of Super Tuesday states. "It's a tough deal for the candidates who are perceived to be at the lower rungs at the moment to figure out where they can get some juice."

Elizabeth Warren, who at one point late last year was tied with Biden in the polls, has stumbled through the early-state votes despite strong debate performances and seems poised to do more of the same in South Carolina. She has insisted, however, that she is prepared to keep up the fight all the way to the convention in July.

Michael Bloomberg is not on the ballot in South Carolina.

Billionaire Tom Steyer, also flailing in the earlier contests, is banking on South Carolina to keep him in the race. He has spent more than $23m on ads in South Carolina, dwarfing what his rivals have spent, making explicit appeals to black voters in the state.

Pete Buttigieg and Amy Klobuchar, both of whom have struggled with African-American voters, are not expected to do well. Earlier strong showings for both candidates came in states where almost all the voters were white, and a poor one among black South Carolinians could call into question each candidate's ability to broaden their base of support to voters of colour, who make up a sizable constituency in the Democratic base.

"It is a big deal" for his campaign if Buttigieg does not perform in South Carolina, said Jim Messina, a top aide on both of Obama's presidential campaigns, because "more people like me are going to say on TV he can't get the minority vote, and that's not helpful to his narrative."

African-American voters, however, may not be the monolith pundits are portraying them as. Just as among Latino and white voters, a generational divide exists that could be a challenge for Biden and a boost for the progressive wing of the party personified by Sanders and Warren.

Former Vice President Joe Biden meets with attendees during a campaign event in Charleston, South Carolina [Matt Rourke/AP Photo]

"We're not that monolithic group that we used to be," said James Felder, an 80-year-old civil rights activist in South Carolina who has always supported Biden. "You've got a whole generation and a half, maybe, who don't know Biden, don't know what has happened in the past."

"This generation," Felder continued, "is more open to others, new faces, as opposed to us who knew what Biden did. We appreciated him as vice president and the fact he served Obama so well, but you've got a generation who's coming along now who says 'Well, that's fine, but let me hear over here, too.'"

With Super Tuesday coming only three days later, the outcome in South Carolina is unlikely to force any of the current candidates out of the race entirely. But strategists say the results are important because they may sway voters elsewhere in the country.

"Anybody who defies expectations and does better than you expect, it just builds a stronger narrative for them," said Matt Angle, a Texas Democratic strategist.