Joe Biden looks on course to secure a campaign-saving lifeline in South Carolina, after a new poll suggested he had a 20 point lead over his rivals.

The poll was published just days before voters in South Carolina, a state where African Americans make up more than half of voters, cast their ballots for a candidate to challenge Donald Trump.

The poll, conducted by New Jersey’s Monmouth University, found the former vice president on 36, a full 20 points ahead of Bernie Sanders, who has emerged as the de facto frontrunner after wins in Iowa, New Hampshire and Nevada.

Billionaire Tom Steyer, who has spent large sums of his own money to reach out to black voters, was placed third in the poll on 15 points.

Of particular interest to Mr Biden, will be the fact he also has by far the largest level of support among African Americans. It suggested the 77-year-old had the support of 45 per cent of black voters, compared to 17 per cent for Mr Steyer, and 13 points for Mr Sanders, the veteran senator from Vermont.

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“South Carolina chooses presidents,” Mr Biden said on Wednesday. “You decided to launch Bill Clinton to the White House, and up to that time, it didn’t look like he was going very far — but you did. You launched my buddy Barack Obama to the White House.”

He added: “I firmly believe, once again on Saturday, you hold in your hands, in South Carolina, the power to choose the next president of the United States.”

Mr Biden’s campaign had always argued that Nevada and South Carolina would be his “firewalls”. After dismal showings in Iowa and New Hampshire, two overwhelming white and largely rural states, he has been counting on strong performance in these much more diverse states to give him a boost ahead of Super Tuesday, when more than a dozen states hold their primaries, including many of those where Michael Bloomberg has spent hundreds of millions of dollars to fund his non-traditional campaign.

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In recent days some polls suggested Mr Biden’s support may be slipping, with some suggesting Mr Sanders was set to continue his momentum. Commentators pointed out that while African American voters in South Carolina, especially older ones, respected Mr Biden because of his experience and because of the eight years he served as Barack Obama’s deputy, it was not without caveat.

Indeed, much of has been based on the presumption Mr Biden has the strongest chance of defeating Mr Trump in November. Yet after bad performances in New Hampshire and Iowa, questions were raised about Mr Biden’s viability. Reports suggest some young African Americans are likely to vote for Mr Sanders.

Earlier this week, Mr Biden secured what was seen as an important endorsement, when congressman Jim Clyburn, the highest-ranking African American in Congress and who represents South Carolina’s sixth congressional district, said he was backing the former vice president.

“I want the public to know that I am voting for Joe Biden. South Carolina should be voting for Joe Biden,” Mr Clyburn said in North Charleston.

“I know Joe. We know Joe. But most importantly, Joe knows us. I know his heart. I know who he is. I know what he is. I know where this country is: We are at an inflection point I am fearful for the future of this country. I’m fearful for my daughters and their future, and their children and their children’s future.”

He added: “It is time for us to restore this country’s dignity, this country’s respect. That is what is at stake this year.”