WASHINGTON – After earning his first top 2 spot in the Democratic race Saturday in Nevada, former Vice President Joe Biden heads to a crucial test in the South Carolina primary, where political experts said a win could breathe life into his flagging presidential campaign – or another loss could end it.

He will be fighting clear front-runner Bernie Sanders, who won the popular vote in the first three nominating contests and performed well among black voters in Nevada's caucuses. Black voters make up the majority of South Carolina's Democratic primary electorate, and polls have long showed Biden with a strong lead among them.

In a speech to cheering supporters in Las Vegas on Saturday evening, Biden was confident: "We're alive, and we're coming back, and we're gonna win. ... I think we're in a position now to move on in a way that we haven't been until this moment. I think we're going to go, we're going to win in South Carolina and then Super Tuesday, and we are on our way."

Biden led polls in the Palmetto State by 20 percentage points last fall before placing fourth in Iowa and fifth in New Hampshire. Biden downplayed those early contests, focusing on more diverse states such as South Carolina, which he argued would better gauge which Democrat should challenge President Donald Trump.

Nevada, which has a significant Latino population, favored Sen. Sanders, I-Vt., in its caucuses Saturday, and Biden placed second. In South Carolina, African Americans traditionally account for more than 60% of Democratic primary voters.

Even as the votes were counted in New Hampshire, Biden flew to rally supporters in Columbia, South Carolina.

“Up until now, we haven’t heard from the most committed constituency in the Democratic Party, the African American community,” Biden said at the time. “So to hear all these pundits and experts, all these cable TV talkers talk about the race, tell them, ‘It ain’t over, man. We’re just getting started.’ ”

Biden, 77, enjoys several advantages in South Carolina. He served eight years as vice president to the first black president, Barack Obama. Biden earlier served 36 years in the Senate, where he worked with state political leaders such as House Majority Whip James Clyburn, D-S.C. And Biden vacations regularly on Kiawah Island.

"Biden has something here that other candidates just don't and can't," said Jordan Ragusa, associate chair of the political science department at the College of Charleston. "I think Biden is still the favorite in South Carolina, but certainly it seems there are cracks in his firewall. It's looking a little more penetrable."

Biden's lead over Sanders narrowed to 4 points by Feb. 18, according to an average of state polls compiled by RealClearPolitics.com. Political experts said polling is fluid and voters are still making up their minds, but a Sanders win would demonstrate his support among minorities and show that Biden couldn't win where his prospects were best.

"Biden really has to stake his claim here," said Robert Oldendick, a political science professor at the University of South Carolina. "I think he has to win. If he does not win in South Carolina, it's pretty much the end of his campaign."

Test for black voters

South Carolina is the first primary contest with a significant black population, a key constituency in national Democratic politics. Voters care most about the economy and the protection of social welfare programs but are less interested in ideological issues such as climate change, according to political experts.

"A lot of people say that African American voters in the South are pragmatists," said Ragusa, who co-wrote "First in the South: Why the South Carolina Presidential Primary Matters." "They are not as attuned to ideological considerations, like voters in the Midwest or Northeast, white or black."

James Hodges, a former South Carolina governor who was national co-chairman of Obama's 2008 campaign, said the state offered a good indicator of who would become the nominee because results in earlier states were muddled in 2008 and 2016.

"South Carolina sort of reset the stage, in large part because of the significance of the African American vote," said Hodges, who is president of McGuireWoods Consulting.

The state's primary Saturday could hint at Super Tuesday results in other Southern states such as Alabama and North Carolina.

"The Super Tuesday states in the South are similar in terms of culture, in terms of the nature of the electorate, with a much higher minority population," Oldendick said. "I don't know that those other early states value the economy as much as voters here."

Divided moderate vote

The South Carolina contest comes at a critical time for Biden. He led an average of national polls for months after announcing his candidacy April 25, 2019.

After the disappointing finishes in Iowa and New Hampshire, Biden fell behind Sanders.

Biden faced challenges in the crowded Democratic field from fellow moderates such as Pete Buttigieg, the former mayor of South Bend, Indiana, and Sen. Amy Klobuchar of Minnesota. Each offered a message seeking to unify the politically polarized country. Neither of Biden's rivals could afford much time in South Carolina as they concentrated on earlier contests.

"They really haven't spent a lot of time in South Carolina of late," Ragusa said.

At the rally in Columbia, Biden repeatedly noted his work with Obama. He promoted his record fighting loan discrimination from banks and his support of voting rights legislation, of historically black colleges and universities and of the Violence Against Women Act.

"We have so much more to do," Biden told the crowd.

During a conference call Thursday with the Black Economic Alliance – a nonpartisan coalition of business leaders who advocate for work, wages and wealth of black Americans – Biden described his priorities for investing in black communities with infrastructure such as broadband. Biden promoted educational proposals, such as doubling Pell Grants for poor students and allowing their use at programs other than for four-year degrees.

“I don’t think anyone deserves the black vote – it’s about earning the black vote,” Biden said. “I have never, never, never, never taken it for granted.”

Asked about his support slipping among blacks, Biden acknowledged that he couldn’t compete with hundreds of millions of dollars spent by two self-funded billionaires in the race: former New York Mayor Mike Bloomberg and Tom Steyer.

“But I can compete by showing up because they know me,” Biden said. “They know my heart, they know my head, they know my record and they know what I’ve done.”

Sanders challenges Biden

Biden faced criticism from more liberal candidates, such as Sanders and Sen. Elizabeth Warren of Massachusetts. Buttigieg and Sanders divided the early contests and were nearly tied in delegates coming out of Iowa and New Hampshire. Sanders won Nevada by a large margin Saturday and took the lead in delegates.

Sanders pays much more attention to South Carolina than in 2016, when Hillary Clinton beat him soundly with nearly three-quarters of the vote. This year, Ragusa said, Sanders has a shot to win because of the fragmented vote among more moderate candidates.

"A strong second-place finish could be just as important as victory in signaling that he could win in a national campaign," Ragusa said. "He really needs to show he is the candidate who can appeal to voters across the spectrum, not just voters in liberal and snowy white states like Iowa and New Hampshire."

Steyer a 'wild card'

Steyer could be a factor after spending $10 million in the state on TV ads, digital ads on Facebook and YouTube and direct mail. Despite missing debates, Steyer edged into third place in the average of South Carolina state polling by RealClearPolitics.

"They are just carpet-bombing the state with ads," Ragusa said.

He distinguished Steyer from Bloomberg because he campaigns in person, shaking hands and talking about reparations for the descendants of slaves, the importance of historically black colleges and universities and social justice.

"African Americans think he's got the right message," said Ragusa, whose hunch is that Steyer eroded Biden's lead among moderates.

"He's the guy to watch, in terms of the wild card," Hodges said.

Bloomberg not on ballot, still a factor

Bloomberg's name won't be on the South Carolina primary ballot. Voters can't write in his name. He's focused on Super Tuesday states that will decide on March 3 more than one-third of the pledged delegates to the Democratic National Convention.

After anteing up nearly $464 million through the end of January, which allowed him to blanket the country with television and digital advertising, Bloomberg's performance in national polls allowed him to join the Nevada debate last week and the South Carolina debate Tuesday. His performance in Nevada was widely criticized.

Hodges said that although Bloomberg isn't competing in South Carolina, his strategy of waiting until later in the nominating process might work.

"The field will be winnowed down for him," Hodges said. "He'll have money and not have been scuffed up in the early primaries."

Uncertainties before primary

The candidates could change some minds before votes are cast.

CBS News will host a debate Tuesday in Charleston, where seven candidates qualified.

As endorsements line up, Clyburn remains uncommitted. He said he wouldn't endorse a candidate before the debate and possibly not afterward. He could influence some votes if he endorses before the primary.

"He's playing it close to the vest and doesn't want the role of 'kingmaker,' " Oldendick said.

Preview of Super Tuesday

Despite the attention paid to Iowa, New Hampshire, Nevada and South Carolina, those four contests choose only 155 pledged delegates to the Democratic National Convention.

South Carolina comes three days before Super Tuesday, when 1,357 out of 3,979 pledged delegates will be chosen in 14 states and American Samoa.

Political experts said a Biden loss in South Carolina would probably knock him out of the race. A win would keep his candidacy alive for bigger states such as California and Texas.

"A good performance will give him a boost," Oldendick said.

Biden’s lead against Sanders narrowed in the latest Winthrop University poll released Friday, and one in five voters remain undecided. Biden is favored by 24% of respondents, compared with 19% for Sanders. The poll of 449 likely voters, which was conducted Feb. 9-19, has a +/- 4.7-percentage-point margin of error.

“Flames seem to be licking through the cracks in Biden’s firewall,” said Scott Huffmon, the Winthrop poll director. “Without a strong showing in South Carolina, Biden’s campaign will be limping into Super Tuesday. Even a win, if not significant and decisive, will be interpreted as a loss by his opponents.”

Ragusa said Biden needs to win by at least 10 points.

"If Sanders does well and come close to Biden, it gives him a legitimate claim to having some of that same crossover appeal, and it undermines Biden's strongest argument going forward," Ragusa said.

Contributing: Jeanine Santucci