LAS VEGAS — Sen. Bernie Sanders won a resounding victory in the Nevada caucuses Saturday, providing another boost to an insurgent campaign that is challenging the Democratic establishment and stifling the plans of rivals who still hold out hope of stopping him.

Sanders’s advantage in Nevada was overwhelming, with substantial leads in nearly every demographic group, allowing him to set down a marker in the first state with a significant share of nonwhite voters. Sanders expanded the electorate by attracting relatively large numbers of first-time caucus-goers, providing momentum as the race shifts into a critical stretch over the next 10 days.

He prevailed among those with college degrees and those without; those living in union and nonunion households; and in every age group except those over 65. He won more than half of Hispanic caucus-goers — almost four times as much support as his nearest rival, former vice president Joe Biden — and even narrowly prevailed among those who identified as moderate or conservative. Despite attacks on his health proposal by the powerful Culinary Union, he won in caucus sites filled with union members.

“In Nevada we have just put together a multigenerational, multiracial coalition, which is going to not only win in Nevada, it is going to sweep this country,” Sanders said during a lively rally in San Antonio, after networks had declared him the winner.

Sanders signaled throughout his speech that he is beginning to see himself as the likely nominee, given his momentum heading toward Super Tuesday on March 3, when 14 states cast their votes. A day after saying he was fighting against the Democratic and Republican establishments, the self-described democratic socialist adopted a more unifying tone.

“We are bringing our people together — black and white and Latino, Native American, Asian American, gay and straight,” he said.

Incomplete results suggested a distant second-place finish for Biden, who has repeatedly predicted he would do well in states with more nonwhite voters. It would be Biden’s strongest showing to date, but it would hardly prove his assertion that he can win states with a large share of minorities.

Biden’s supporters asserted he was a “comeback kid,” even though he had led the polling in Nevada until 10 days ago. “Y’all did it for me,” he told a group of supporters at a union hall here. “I ain’t a socialist. I’m not a plutocrat. I’m a Democrat, and proud of it.”

Former South Bend., Ind., mayor Pete Buttigieg and Sen. Elizabeth Warren (Mass.) seemed likely to finish far back, reflecting an ongoing fracture among those seeking to present a clear alternative to Sanders.

Buttigieg used his caucus-night speech to launch a far more pointed attack on Sanders than he has previously, warning that the party it is marching down a dangerous path.

“Before we rush to nominate Senator Sanders in our one shot to take on this president, let us take a sober look at the consequences,” Buttigieg said, adding that the senator from Vermont “believes in an inflexible, ideological revolution that leaves out most Democrats, not to mention most Americans.”

Such attacks may increase now that Sanders has such momentum, having won the most votes in the first three states. Rivals are increasingly taking aim at his Medicare-for-all plan and his refusal to release medical records, given that he is 78 and suffered a recent heart attack. In recent days, Sanders has been forced to respond to a Washington Post report that U.S. intelligence officials briefed his campaign that Russia is trying to help it.

No candidate signaled he or she would drop out so that moderates could consolidate their forces. That leaves Sanders in a position to leverage a healthy campaign account and a grass-roots army to amass an even larger lead as the contest shifts toward delegate-rich states such as Texas and California.

Nevada Democratic officials had hoped to avoid repeating the disaster that engulfed the Iowa caucuses, where technological and organizational failures prevented results from being released on caucus night, and where the outcome still has not been finalized.

Some precinct leaders did report a lack of caucus-day volunteers, and others had difficulty reporting the numbers using a special hotline. It was unclear late Saturday when the results would be finalized, but the system was operating well enough to make clear that Sanders had won easily.

Biden was hoping to stabilize his campaign following dismal finishes in Iowa and New Hampshire, and for days he had been suggesting a second-place win in Nevada would amount to a victory. He has held a significant advantage in South Carolina, which holds the next vote on Saturday, though Sanders has been eating into his lead there.

Warren had a standout performance in the most recent Democratic debate, interrogating former New York mayor Mike Bloomberg and aiming zingers at her other rivals, but it came after tens of thousands of early votes had already been cast in Nevada and was not enough to give her an impressive finish.

Still, Warren’s campaign manager pointed to numbers suggesting her support climbed after the debate. “We believe the Nevada debate will have more impact on the structure of the race than the Nevada result,” Roger Lau wrote on Twitter. “Since a huge percentage of the votes were cast before the debate — likely well more than half — tonight’s results are a lagging indicator of the current state of the race.”

“I’ve got a word for Nevada,” Warren said in Seattle. “Thank you for keeping me in the fight.”

Her speech mostly focused on Bloomberg, including poking fun at his height by saying she wanted to talk about a “big threat.” “Not a tall one,” she said. “But a big one: Michael Bloomberg.”

The state’s caucuses were also the first test of whether Buttigieg, as well as Sen. Amy Klobuchar (Minn.), could expand their appeal beyond the white voters that paved their path to success in Iowa and New Hampshire. The entrance polls indicated that they were still struggling, with no more than 3 percent of black voters surveyed supporting them.

Bloomberg, whose barrage of ads has bought him a presence in the race but whose shaky debate performance raised questions about his longevity, did not enter the Nevada contest. He will be making his first appearance on the ballot on Super Tuesday.

The results did little to elevate any candidates as the alternative to Sanders. Warren announced she had raised $14 million following the New Hampshire primary, and Klobuchar also raised a large sum following her surprising third-place finish in New Hampshire. Both candidates also have new super PACs supporting them.

“As usual, I think we have exceeded expectations,” Klobuchar told supporters in Minneapolis, though results are showing her heading toward a sixth-place finish in Nevada. “A lot of people didn’t even think I’d still be standing at this point.”

The Nevada caucuses came at a crucial moment as the race began barreling out of the early nominating states, where most of the focus has been the past year, and toward a far more nationalized contest that could benefit those with money and momentum.

Even as the results were coming in here, most of the candidates had already left Nevada to campaign in some of the 14 states that will vote on Super Tuesday and beyond. Warren headed to Seattle, Buttigieg to Colorado, and Sanders to Texas.

Biden was one of the few who stayed in the state, a reflection of how tightly focused his campaign was on trying to rebuild after the devastating losses in Iowa and New Hampshire. He is also the only candidate planning to campaign solely in South Carolina in the coming week, focusing on a state that is now vital to preventing his third presidential campaign from ending in disappointment.

“We’re alive and we’re coming back, and we’re going to win,” Biden said Saturday night, before declaring plainly: “We’re going to win in South Carolina.”

As he visited a caucus site Saturday, Biden laughed when a reporter asked how he would beat Sanders if the senator from Vermont won Nevada.

“I beat him by . . . just moving on,” he said. “People want to know who’s the most likely to beat Donald Trump. And even the few polls that show Bernie tied with me or ahead of me, show me being the one that is most likely to be able to beat Trump.”

The entrance polls showed Sanders got 23 percent among those who prioritized beating Trump, compared with 19 percent for Biden.

Sanders’s strong support among liberals, younger voters and supporters of single-payer health care helped fuel his advantage, according to preliminary entrance poll results.

A clear majority supported Sanders’s signature policy of replacing all private health insurance with a single government plan for everyone, and Sanders dominated with this group.

Nearly 75,000 people participated in early voting, and more filed into caucus sites around the state Saturday morning. The final vote was expected to exceed the 84,000 who participated in 2016, but was unclear whether it would top the 118,000 from 2008. Democrats were nervous after the Iowa caucuses failed to generate a large turnout but were comforted by a record turnout in New Hampshire.

David Weigel contributed to this report.