CHARLESTON, S.C. ― It’s come to this: Former Vice President Joe Biden badly needs a primary victory to keep alive his chances of winning the Democratic nomination, and his firewall state of South Carolina is finally heading to the polls later this week.

But in a place where he once looked unassailable (with support as high as 46% at one point), Biden is suddenly facing a competitive fight as other candidates in the race continue to make inroads with Black voters, his core constituency.

A disappointing finish here would be devastating to his campaign and his path forward, especially after repeated assurances from his staff that he was positioned to do best in more diverse communities like those in the Palmetto State.

“It’s not looking great. He has the opposite of momentum,” South Carolina Democratic strategist Tyler Jones told HuffPost. “He’s gotta win South Carolina convincingly to stay in the race. Expectations are also very high for him, which they set for themselves. It’s win or go home for him.”

Ethan Miller via Getty Images It's "win or go home" for Joe Biden in South Carolina.

In the Nevada caucuses over the weekend, Biden is projected to come in a distant second behind Sen. Bernie Sanders (I-Vt.), whose decisive win there solidified his status as the front-runner in the race. It was a badly needed finish for Biden after poor showings in the first two contests in Iowa and New Hampshire. Still, his chances of stopping Sanders, who is on track to take a huge delegate lead in the Super Tuesday primaries early next month, will hinge on how well he does in South Carolina.

Biden’s support in the state has fallen by double digits in recent weeks, however. According to a CBS News poll released Sunday, the former vice president leads Sanders by only 5 points, 28% to 23%. Sanders and billionaire environmentalist Tom Steyer, who has 18% support in the poll, have made sizable gains in the state, especially with its large population of Black voters.

“I feel good about where we are. I feel good about going into South Carolina,” Biden told CBS’ “Face the Nation” in that aired Sunday. “And I feel good about the kind of support I’ve had with African Americans around the country.”

Steyer, in particular, has put significant time and money into the state’s Democratic primary. His campaign has essentially had the airwaves to itself for months, spending millions on TV and radio ads. He’s scheduled to hold many events in the state this week and will appear on stage at Tuesday’s Democratic primary debate in Charleston. Even if he doesn’t win, however, Steyer could stand in the way of Biden winning in a total blowout.

“Tom Steyer could play spoiler in the South Carolina primary,” Jones added. “I never thought I’d say Biden’s career could be ended by Tom Steyer, but here we are.”

Alex Wong via Getty Images Tom Steyer could spoil Biden's victory party in South Carolina.

Biden had a strong performance in last week’s primary debate in Las Vegas, joining in on attacks on billionaire former New York City Mayor Michael Bloomberg over his administration’s stop-and-frisk policy. It may have been his best debate yet, yielding strong fundraising for his struggling campaign. He’ll need to post another good showing at Tuesday’s debate in Charleston in order to fend off Steyer and Sanders and prove he can win a primary.

At a campaign stop in South Carolina on Sunday, Biden took jabs at Steyer over his hedge fund’s past investments of millions of dollars in the nation’s leading private prison corporation.

“I’m not saying Tom Steyer’s a bad guy, but Tom Steyer was one of the largest investors in private prisons in the United States of America while I was trying to get rid of private prisons and Barack was trying to get rid of private prisons,” Biden told reporters, referring to the former president.

Biden has also begun to sharpen his criticisms of Sanders, whose path to the nomination is getting clearer by the day. Last week, he criticized the senator for his past votes against gun control measures in the 1990s, including the Brady Act, which mandated federal background checks and a waiting period for some handgun purchases. Though Sanders now supports gun control measures, Biden is likely to use a similar strategy and focus on gun violence prevention in Charleston, the site of an infamous 2015 church shooting.

What could trip up the vice president this week is a New York Times report about a story he’s been telling on the campaign trail in recent weeks: that on a visit to South Africa decades ago, he tried to visit Nelson Mandela in prison and got arrested. The Times was unable to verify the claim about his arrest, and Biden’s campaign has notably not responded to queries about it.

But a highly influential endorsement could boost Biden’s chances in South Carolina ahead of Saturday’s primary vote. House Majority Whip Jim Clyburn (D-S.C.), who is the highest-ranking Black member of Congress, is expected to announce his preferred choice to lead the Democratic Party on Wednesday, and it’s likely it’ll be Biden.

Appearing on ABC’s “This Week” on Sunday, Clyburn expressed concern about the prospect of nominating Sanders due to how it might impact Democrats’ chances of retaining the House and recapturing the Senate in November.

“I think it would be a real burden for us in these states or congressional districts that we have to do well in,” Clyburn said in the interview. “If you look at how well we did the last time ... these were not liberal or what you might call progressive districts. These were basically moderate and conservative districts that we did well in. And in those districts, it’s going to be tough to hold on to these jobs if you have to make the case for accepting a self-proclaimed democratic socialist.”