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CHARLESTON, S.C. — Bernie Sanders is heading on Saturday into South Carolina, the state that broke him in 2016, stronger than ever after a razor-thin second-place finish in Iowa and wins in New Hampshire and Nevada.

"I just think there's one big, huge, screaming story here tonight, and that is that there is a front-runner in the 2020 Democratic presidential race," veteran Democratic strategist James Carville, a vocal critic of Sanders, said on MSNBC. "We're in a whole new ballgame here, and ... some of these candidates are going to have to make really hard decisions about who stays in and who gets out and where we go from here."

But the heat will be on like never before for Sanders, the independent senator from Vermont who describes himself as a democratic socialist, as his doubters and detractors scramble to try to stop him and the race's former front-runner, Joe Biden, tries to reclaim that position with a second-place showing in Nevada and a promise to win South Carolina.

"We're alive, we're coming back, and we're going to win," Biden told supporters at a union hall in Las Vegas. "I ain't a socialist. I ain't a plutocrat. I'm a Democrat — and proud of it."

South Carolina's primary Saturday will come just three days before Super Tuesday, March 3, when 40 percent of the delegates in the entire primary contest are up for grabs.

Many candidates skipped out of Nevada early to campaign in places like Texas, California and Washington, and they'll use South Carolina to hit East Coast Super Tuesday states like Virginia and North Carolina.

Four years ago, Nevada halted Sanders' momentum and South Carolina reversed it when Hillary Clinton crushed him here, exposing a weakness with voters of color that would prove fatal to his 2016 presidential campaign.

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But years of organizing and a retooled message are bearing fruit for Sanders.

He handily won Latinos in Nevada, where his campaign had been advertising on Spanish-language radio and to Latin music listeners on Spotify for months, and he came a close second to Biden among African Americans, according to NBC News entrance polls.

In South Carolina, where African Americans will make up a majority of Democratic electorate in Saturday's primary, the commanding 20 percentage-point lead Biden enjoyed last fall has been whittled to less than 4 points over Sanders in polling averages.

Clay Middleton, a Democratic strategist who ran Clinton's campaign in South Carolina, was planning to vote early for Biden two weeks ago — but he then decided to hold off. "I don't know what it was. It just didn't feel right," he said.

Now he wants to wait and see what happens in Tuesday's debate here. "I'm undecided," he said. "My wife is undecided. My immediate family and good friends are all undecided."

That could spell trouble for Biden in a state that is supposed to be his firewall, and it focuses attention on his performance in the coming debate.

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Still, Antjuan Seawright, a Columbia-based Democratic consultant, said the state remains Biden's to lose. "I think this is honestly a race for second place," he said.

That competition is likely between Sanders and California billionaire Tom Steyer, who has been a non-factor in other states and didn't qualify for last week's debate in Las Vegas. He is polling in third place here, just behind Sanders.

Other campaigns have largely written off South Carolina given Biden's perceived strength, but Steyer has invested heavily here and in outreach to African Americans elsewhere. He came in third among black voters in Nevada, even though he's polling at just 2 percent among all Democrats nationally.

"I can't see how Steyer justifies staying in after getting zero delegates in the first three states," said Brady Quirk-Garvan, former chairman of the Charleston Democrats. "At this point, moderate candidates who don't see a path to win but are staying in are just helping to create a Sanders nominee, and that scares a lot of South Carolinian Democrats."

Many red-state Democrats are worried that Sanders would make it impossible for the party to win in more conservative states like this one.

But the rest of the field is splintered and shows no signs of going anywhere before Super Tuesday, making it more likely that Sanders will be the only candidate to consistently cross the 15 percent threshold needed to win delegates in coming contests.

One big wild card is whether billionaire former New York Mayor Michael Bloomberg will start running negative ads against Sanders. So far, he's attacked only President Donald Trump. But some Democrats say massive spending from Bloomberg is the only thing that could stop Sanders now for the nomination.

Asked about the possibility after last week's debate, Howard Wolfson, a top Bloomberg adviser, said the campaign had no immediate plans, but he added, "Campaigns are fluid. We'll see."

CORRECTION (Feb. 23, 2020, 6:35 p.m. ET): An earlier version of this article misspelled the first name of a South Carolina Democratic consultant. He is Antjuan Seawright, not Antjean Seawright.