(CNN) The next nine days will determine whether Bernie Sanders can bring the Democratic presidential race to a quick and decisive end -- or if it's time for the party to brace for a months-long and potentially divisive battle for the nomination.

After a massive victory in Nevada , the Vermont senator is now positioned to potentially land knockout blows by delivering a win in South Carolina, and then amassing a clear lead on March 3, when 14 states and American Samoa vote. Sanders argues the diverse movement he is building, proven by his winning coalition in Nevada, and his platform of progressive policy proposals are the key to defeating President Donald Trump in November.

But his emergence as the Democrats' undisputed front-runner has set off alarm bells among the party's establishment and intensified the attacks from his moderate rivals, who argue that the Vermont senator's agenda risks handing Trump four more years in the White House. Democratic primary voters have not coalesced around an alternative candidate to Sanders, however, undermining any potential effort to stop him.

The trajectory of the Democratic race will be shaped over two days of CNN town halls and a debate this week in Charleston -- then in Saturday's South Carolina primary and on Super Tuesday three days later.

Former Vice President Joe Biden is making what could be his last stand in South Carolina. Biden has long led the polls in a state he's identified as his firewall, bolstered by overwhelming support from the African-American voters who make up more than half the state's Democratic electorate.

If he's able to land a decisive victory, it could propel Biden ahead of a jumbled pack of moderates vying to get into a one-on-one contest with Sanders.

But three straight losses have raised questions about whether Biden can hang on in what should be his strongest state. And without a win in South Carolina, Biden would have no real path forward -- going into Super Tuesday with a campaign far behind his rivals in fundraising and with no momentum.

The race's biggest question mark could be Massachusetts Sen. Elizabeth Warren , who eviscerated former New York Mayor Michael Bloomberg in last week's debate in Nevada -- but did it too late to affect the results there, since the majority of the state's Democratic voters had cast their ballots early, before they saw Warren's performance.

The sudden switch from retail politicking across the Palmetto State, with occasional forays into nearby Super Tuesday states like North Carolina and Virginia, over the next six days to an all-out sprint across the country in the three days that follow will define the Democratic race.

To compete in what's about to become a national contest, candidates need much more money and momentum than Iowa, New Hampshire, Nevada and South Carolina require.

Bloomberg -- who hasn't been on the ballot in the early states, but turned in a disastrous debate performance in Nevada and will be on stage again in South Carolina -- has already spent $160 million on television ads in Super Tuesday states. Steyer has spent more than $38 million.

But beyond them, all advertising from major candidates has been surgical, rather than the sort of broad-based campaign aimed at reaching every voter in key states. Sanders has spent the most, at $10 million. Biden and Buttigieg have spent nothing.

Can Biden's firewall hold?

A CBS/YouGov poll of South Carolina released Sunday showed Biden in the lead with 28% support, followed by Sanders at 23%.

But Biden's rivals are threatening that lead: The Sanders campaign launched an ad in South Carolina recently touting the support of Richland County Council Vice-chair Dalhi Myers, an African-American woman elected official, who switched her support from Biden to Sanders last month.

"I want to see people motivated to get out and vote for a candidate that they believe in," Myers said. "This campaign's got the movement. We've got the momentum."

Billionaire businessman Tom Steyer has also become a thorn in Biden's side in South Carolina. Steyer, who has focused for months on winning over black voters in South Carolina, qualified for Tuesday's debate stage. And the CBS/YouGov poll showed him with 18% support there -- much of which appears to have been siphoned away from Biden.

Biden complained on CBS' "Face the Nation" Sunday about "the amount of money being spent by the billionaires to try to cut into the African-American vote."

But he's also left no doubt: His only chance at competing with Sanders is to win in South Carolina.

"Whomever wins this primary is going to go onto Super Tuesday very strongly, and I think it's going to be Bernie and me going into Super Tuesday," Biden told reporters after a church visit in North Charleston on Sunday.

Sanders faces heightened scrutiny

The focus of the next nine days is Sanders.

In Nevada, entrance polls showed he dominated among young voters, Latinos, liberals and independents, and fought to a draw among moderate and conservative voters and those focused on electability. Those results offered the clearest glimpse yet at Sanders' emerging coalition -- which, if it holds on Super Tuesday, when one-third of all Democratic delegates are on the line, could put him far enough ahead that no other candidate can catch him.

So his rivals -- perhaps too late -- are taking Sanders on much more aggressively.

Biden, in his caucus-day speech in Nevada, highlighted Sanders' reported consideration of a primary challenge against then-President Barack Obama in 2012. He said he was proud to be Obama's vice president. "And I promise you, I wasn't talking about running in the Democratic primary against him in 2012," Biden said.

Buttigieg warned Saturday that Sanders could be close to developing "an insurmountable lead." Then on Sunday, he intensified his attacks on Sanders.

"I respect my friend, Sen. Sanders," Buttigieg said at a large rally in Northern Virginia on Sunday. "I believe the ideals he talks about our ideals we all share. But I also believe that the way we will build the movement to defeat Donald Trump is to call people into our tent, not to call them names online."

Buttigieg, miles from the United States Capitol, then reflected concerns among some candidates and operatives in down-ballot races that Sanders at the top of the ticket would hurt their chances in November.

"We dare not ignore, we dare not dismiss and we absolutely dare not attack those voices in the Democratic Party focusing on keeping those seats in the right hands," Buttigieg said.

He also began airing an advertisement attacking Sanders' signature "Medicare for All" proposal last Friday in South Carolina.

"Bernie Sanders' Medicare for All would completely eliminate private insurance, forcing 150 million Americans off their current plans -- including 20 million seniors on Medicare Advantage," the narrator says. "Pete Buttigieg has a better way to lower costs and cover everyone."

South Carolina is where Sanders' 2016 campaign got wiped out and never truly recovered. Clinton defeated him there in every county, by a staggering 47.5 percentage points, 73.5% to 26%, overall.

For Sanders, victory in South Carolina would amount to a resounding rejection of the narrative that he can't appeal to the party's most loyal base of support -- African American voters -- and validate its efforts to raise his profile in communities of color.

If Sanders finishes a close second, he will likely enter Super Tuesday with the wind still at his back. But a more disappointing result could further escalate concerns among Democrats over his viability in a general election.

So far, Sanders is largely ignoring his rivals' attacks -- instead making the case that he is the party's most electable general election candidate.

Campaigning in Houston on Sunday, Sanders read the results from the CBS/YouGov poll showing him as the strongest Democratic candidate in head-to-head match-ups with President Donald Trump

He told the crowd he's positioned to land a knockout blow.

"If on Tuesday we can bring out working people, and young people, people who have given up on the political process, people of all shades who believe in economic justice, social justice, racial justice, environmental justice -- if we can create a large voter turnout -- we're going to win Democratic primary a week from Tuesday," Sanders said.

Will the field narrow?

Those vying to get into a one-on-one race with Sanders first have to separate themselves from a pack of candidates that hasn't been winnowed at the top in the first three contests.

Warren is focusing on Super Tuesday states, and Warren in Seattle on Saturday night sharpened her criticism of Sanders over his support for keeping the Senate's filibuster in place.

"I say Mitch McConnell is not going to get a veto over what we want to do," she said.

Buttigieg, meanwhile, is still in a battle with Biden and others to become the moderate alternative to Sanders -- but is damaged by his inability to win large numbers of non-white voters.

The candidate in the most jeopardy appears to be Minnesota Sen. Amy Klobuchar , who finds her campaign at a perilous point heading into South Carolina.

The Minnesota senator bucked expectations in New Hampshire, finishing in a surprising third place. The finish imbued her campaign with momentum, but also highlighted a key issue: A lack of a serious infrastructure in Nevada and the inability to win over black or Latino support.

Klobuchar's momentum did nothing for her in Nevada, where with half the results in, she's in the low single digits. Klobuchar has just 25 staffers on the ground in South Carolina, after having 50 in Nevada.

"We have a long way to go," Klobuchar's campaign manager Justin Buoen tweeted on Saturday.

But Klobuchar's electoral argument is now dwindling further and faster than any of the other top candidates, as the same aides that frantically looked to dispatch staffers to Nevada try to salvage the senator's campaign in South Carolina.

Even with the difficult road ahead, Buoen told CNN on Sunday that "throughout this race, our campaign has exceeded expectations and I have no doubt we'll continue to do so."