YEMASSEE, South Carolina — In California and around the country, former San Francisco hedge fund chief Tom Steyer has struggled to become more than an afterthought in the presidential race.

But in South Carolina, where Steyer has poured millions of dollars into ads that have made him an unavoidable presence to anyone with a television, he’s become a top-tier contender with the potential of shaking up the race for the Democratic nomination.

Polls have found Steyer in third place in South Carolina, behind former Vice President Joe Biden, whose campaign has long viewed the state as his firewall, and Sen. Bernie Sanders, who is riding a wave of momentum after his blowout win in last week’s Nevada caucuses.

When South Carolina votes on Saturday, Steyer could quickly become Sanders’ favorite billionaire.

Moderate Democratic leaders are panicking that Sanders could win the first-in-the-South primary, putting the democratic socialist on a glide path to the nomination — and polls show that Steyer is winning the support of black voters who had previously backed Biden, likely making Sanders’ path to victory easier. After Steyer’s distant fifth-place showing in Nevada, he’s facing new pressure to drop out of the White House race.

“In South Carolina, Tom Steyer is probably Bernie Sanders’ biggest supporter,” said Brady Quirk-Garvan, the former chair of the Charleston County Democratic Party. “Every vote that Steyer is gaining here just helps boost Bernie.”

But as he campaigned across the state’s Lowcountry region on Sunday and Monday, speaking before African-American church groups in rolled-up shirt sleeves and his trademark plaid tie, a defiant Steyer argued he can win South Carolina.

“I don’t think anybody owns people’s votes, in South Carolina or anywhere else,” he told reporters after being asked whether he was draining support from Biden.

Steyer — the last Californian standing in the presidential race — spent millions in all four of the early primary and caucus states. But while the other contenders competed intensely in Iowa and New Hampshire, Steyer was all but alone on the South Carolina airwaves over the last few months — giving him the opportunity to take advantage of Biden’s drop in support. Now, as he’s received encouraging poll numbers, he’s doubled down on the state, and hopes that a strong showing here will give him enough momentum to keep his campaign alive.

As of this weekend, he’d spent more than $21 million on TV ads in South Carolina, about four times as much as all of his rivals combined. He’s also held more South Carolina events than any other current candidate, according to a tally by the Charleston Post and Courier. His wife, Kat Taylor, has even temporarily moved to the state, renting a home in the capital, Columbia, for the last three weeks before the election.

For some Palmetto State voters, it seems like it’s hard to play a YouTube video without Steyer popping up in an ad, or to open their mailboxes without seeing the billionaire on another glossy mailer. According to a CBS News poll released Sunday, 91 percent of likely Democratic primary voters in the state have seen his ads.

Many of the attendees who showed up at Steyer’s event in Hampton — a rural town of 3,000 people named after a Confederate general — said they came in part just to see his familiar face in the flesh.

“I open my mailbox, and it’s all Tom Steyer,” said Deitre Lawton, 54, an activist for people with Down syndrome, who plans on voting for him. “Tom Steyer and bills.”

“He looks younger here than on TV,” mused Juanita Boles, who’s still making up her mind on whom she’s supporting.

Steyer’s campaign has focused heavily on black voters, who typically make up about 60 percent of the Democratic electorate, and were integral to Barack Obama’s victory here in the 2008 primary and Hillary Clinton’s in 2016.

More than 90 percent of the roughly 100 Steyer staffers who’ve been organizing in the state in recent months are African-American and South Carolina natives, with about half working “within 10 miles of where they were born,” said Brandon Upson, the campaign’s national organizing director, who’s based in the state.

His campaign has spent tens of thousands of dollars on advertising in black newspapers in the state, donated to other local black organizations, and made a point of hiring African-American-owned catering companies for his events.

“He’s put his money where his mouth is,” said State Rep. Michael Rivers, one of Steyer’s endorsers.

Steyer has also rolled out proposals like investing $125 billion in historically black colleges and universities. When he spoke Sunday at a Pentecostal church built on the edge of a tendril of marshland stretching inland from the Atlantic, one of Steyer’s biggest applause lines was his declaration that he’s the only candidate to support reparations for slavery. (Most other Democrats have called for the issue to be studied.)

“Certainly, his money has made a big impression,” said Gibbs Knotts, a political science professor at the College of Charleston and the co-author of a book on the South Carolina primary. “But he’s also come to the state, had meaningful conversations with people, and really put together an agenda that I think addresses the concerns of African-American voters.”

That has helped him cut into the heart of Biden’s most important voter base. Between November and February, Biden’s support among likely black primary voters in the state had dropped from 54 percent to 35 percent, while Steyer’s jumped from 2 percent to 24 percent, according to CBS polls.

“People said (Biden) had a firewall, but he didn’t earn that,” Upson argued in an interview. “If you subtract Obama from Biden, who are you voting for? Many people in this state can’t answer that question.”

Several voters who came to Steyer’s events said they had switched from backing the former vice president to the billionaire.

“I would have been with Biden, but he seems like he’s slowing down these days,” said James Jackson, 71, a retiree from Varnville, as he stood in line for a photo with Steyer. He said he loved Steyer’s ads, especially the ones where Steyer talks about how he can beat Trump on the economy.

Biden has started striking back, criticizing Steyer Sunday for his past investments in private prison companies. (He has since divested.) Steyer could face more attacks during Tuesday’s debate in Charleston, which he qualified for Sunday.

On the campaign trail, Steyer has taken some shots at Sanders, contrasting his business record with what he described as the Vermont senator’s support for public takeovers of the health insurance and energy industries. “I don’t think I want Bernie Sanders running my electrical system,” Steyer said in Hampton. “That is a scary concept.”

And Steyer’s fire-hose spending in the state has also attracted scrutiny. Some local officials have called him out for hiring multiple state legislators on his payroll, although Sanders’ campaign has done the same.

“If you’re getting 50, 60 thousand dollars, it’s fair to ask if you really think this is the best person for the job, or if it’s just because you’re on the payroll,” Quirk-Garvan said.

Steyer and his supporters have strongly pushed back, with the candidate saying Sunday that that criticism “has a racist overtone to it.”

“We are paying people for actually going out and doing outreach,” he said. “That’s how grassroots works, and the idea that if in fact it’s black people, somehow it’s become corrupt, I don’t accept that.”

Steyer’s campaign has also spent thousands of dollars on businesses and nonprofits owned or run by other prominent South Carolina political figures — such as $40,000 to rent its Columbia office from a real estate company owned by the daughter of Rep. Jim Clyburn, the state’s most influential Democrat. The payments were first reported by The New York Times.

Earlier this month, one of the largest African-American congregations in the state also applied for funding from Steyer and his wife’s charitable foundation. Taylor told the Associated Press that the group will only act on the proposal after the primary, in order to avoid the appearance of a conflict of interest.

And requests for financial help keep coming. At one of his campaign events on Sunday, Tom Jenkins, a local planning commissioner, asked Steyer if he would fund renovations to a dilapidated old high school building. Jenkins, 78, was in the last class to graduate from the segregated school before it closed when the district integrated in 1970.

“I think this is the closest in my lifetime I’m ever going to get near a billionaire,” Jenkins told Steyer.

“It’s not that exciting,” the candidate quipped in response. He didn’t make a commitment to fund the project, but said he wanted to keep helping people like Jenkins whether he made it to the White House or not.

“There’s no way I’m not coming back to South Carolina,” Steyer vowed. “I’m not going to disappear.”

How much longer he can stick in the race for the nomination is turning out to be a much bigger question.