Sanders has a massive head start in money and organization, and is looking to notch a big win in California.
And the rest of the field is left scrambling to prove they belong in the race.
Former South Bend, Indiana, Mayor Pete Buttigieg is looking for a foothold anywhere. And former New York Mayor Michael Bloomberg will appear on the ballot for the first time after skipping Iowa, New Hampshire, Nevada and South Carolina -- but is doing so with his core rationale for running now in question.
Here are six takeaways from South Carolina's primary:
Can Biden’s big win narrow the field?
Biden didn't just need a win in South Carolina -- he needed the kind of massive margin of victory that would consolidate the field and send the message to Democratic voters and donors that he's the party's strongest Sanders alternative.
Biden's most important asset remains his support from older African American voters. It was his "firewall" in South Carolina. And more importantly, it could buoy him across the South on Super Tuesday. Alabama, Arkansas, North Carolina and Tennessee -- as well as parts of Texas -- have similar demographics that could help Biden keep the delegate count close to Sanders.
In 2008 and 2016, black voters were the decisive in the Democratic presidential primaries -- first for Barack Obama, then for Hillary Clinton. And in both races, blowout victories in South Carolina were the first indications of what would follow.
This is a different year, and while Biden won 64% of black voters, according to exit polls, his advantage isn't quite as clear. The field is much more fractured, with Sanders having made inroads with African American voters over the last four years and Bloomberg looming Tuesday.
But if Saturday's victory gives Biden a boost with those voters, it would propel him back into serious competition in a race many had all but counted him out of just a week ago.
Sanders hits a major road bump
South Carolina pumped the brakes on Sanders' drive to the nomination.
The Vermont senator came to the Palmetto State hoping that he could keep the race close and, at the least, show a significant improvement on his performance in 2016, when Hillary Clinton beat him by 47 percentage points.
Sanders fared better this time around, but his still distant second place finish on Saturday will raise new questions over his ability to win the support of older African American voters, a key constituency for any Democratic candidate.
Perhaps more concerning for Sanders is the potential that moderates -- after splintering in the first few contests -- are beginning to coalesce around Biden, who almost completely swept the race-within-a-race among the anti-Sanders crowd.
The bright spot for Sanders: Super Tuesday is only two days away, and states like California and Texas began voting well before these results came in. His momentum could survive even as his South Carolina dreams are dashed.
Bloomberg’s rationale in question
Bloomberg's $500 million in spending has made him a major player on Super Tuesday, when he'll be on the ballot for the first time.
But Biden's performance Saturday begs basic questions about his candidacy: Why is Bloomberg doing this? And why should any voter consider him?
His late entrance in November was motivated by a belief that Biden was weak and no one else could compete with Sanders. On Saturday, Bloomberg campaign manager Kevin Sheekey insisted he wouldn't exit the race after Biden's strong showing.
"Mike Bloomberg has not been on the ballot yet," Sheekey said in a statement. "Our campaign is focused on organizing Democrats and building infrastructure in states all around the country. Mike is the only candidate to campaign in all fourteen Super Tuesday states over the last two months and we look forward to Tuesday."
Now that Biden's "firewall" has held and he enters Super Tuesday with momentum, Bloomberg's presence in the race more realistically will have the effect of splitting the non-Sanders vote and making it easier for the Vermont senator to build a big delegate advantage.
Bloomberg has surged in national polls, and has chipped into Biden's support among black voters. Whether that survives South Carolina's result -- and how Bloomberg handles the three days -- bears closely watching.
Warren is still looking for her base
Warren's pitch during this week's debate was simple: If you like progressive policies but are unconvinced that Sanders can bring them to fruition, I'm your candidate.
But in South Carolina, like the states before it, Warren finished way off the pace. She will enter Super Tuesday without a single top-two finish over the first four contests.
Warren has pitched herself as the only person in the field who can unite the Democratic Party's warring ideological factions, and that might yet be the case, but she now faces a scenario in which moderates could flock to Biden and progressives harden their support for Sanders.
That doesn't leave much space -- or many votes --- for Warren, who despite being a popular figure with many Democrats, has not in this primary shown the ability to turnout a reliable base of support.
Any efforts to win over Sanders voters appear to have gone by the wayside, too, as she continues to shellack him on the stump. In Houston Saturday night, she described Sanders as a senator "who has good ideas, but whose 30-year track record shows he consistently calls for things he fails to get done, and consistently opposes things he nevertheless fails to stop."
The good news for Warren: Money.
She isn't running out of it anytime soon. After a recent surge in fundraising and with a big-spending super PAC providing air cover, she can afford to see how Super Tuesday and the subsequent contests unfold.
Paths narrowing for Buttigieg, Klobuchar
South Carolina was the worst-case scenario for Buttigieg and Klobuchar.
Neither of the two candidates were ever able to figure out South Carolina and it showed on Saturday. But Biden also romped in the state, providing his campaign with much-needed momentum that could threaten the justification both Buttigieg and Klobuchar have long used for their campaigns.
Both candidates have long struggled with black voters, a deficiency that imperiled their runs in a state where nearly 60% of the electorate was black, according to exit polls. Buttigieg tried to win over black voters with a range of events in the state, while Klobuchar spent barely any time in South Carolina in the week leading up to the state's primary.
Neither strategy worked, and now the two candidates are limping into Super Tuesday, with their paths to the presidency as narrow as they have ever been.
Buttigieg's campaign is lowering expectations for March 3, with a senior aide describing their strategy as "limiting Sen. Sanders' lead and making sure that it is possible for an opposing candidate to close that gap in the remaining states." Buttigieg's team will aim to reach viability -- 15% of the vote -- in key districts but are up front about the fact that it doesn't expect to win a single state on March 3.
A top Democrat close to the Buttigieg campaign told CNN Tuesday night that the former mayor is studying whether he has a path forward. He hasn't reached a conclusion -- or if so, he hasn't talked about it openly, even among his small circle of advisers. Buttigieg's team knows that how he leaves the race -- if it comes to that -- is important to his future.
For Klobuchar, the focus on Super Tuesday started days before South Carolina even voted, with the candidate headlining events in North Carolina, Virginia, Tennessee and Maine this week, compared to one public event in South Carolina this week. Klobuchar's top aides believe she can withstand a significant loss in South Carolina and rely on the $4.2 million they plan to spend on ads in Super Tuesday states.
But those plans must now confront a new reality: Increased pressure on both of them to get out of the race.
With Biden surging and Sanders benefiting from a fractured field, the pressure on both Buttigieg and Klobuchar to end those campaigns will be more intense than ever, with both candidates having to justify their paths forward in the coming days.
Steyer exits the race
Steyer went all in on South Carolina and it didn't work out.
Steyer ended his campaign on Saturday, closing out a late entry bid where the billionaire spent more than $200 million on television and radio ads.
South Carolina was a disappointment for Steyer. The billionaire businessman had hoped that his that his $22 million on television and radio ads in the state -- along with his oft touted support for reparations for slavery -- would cut into Biden's support among black voters.
That didn't happen and the failure doomed his campaign.
The question now for Steyer, who was a prolific Democratic donor before he ran for president, is what he will do with his massive wealth in the run against Trump this year.