Biden's attack during an interview for NBC's "Meet The Press" came as he fights to rescue his struggling presidential bid and Sanders works to strengthen his strong standing with the contest speeding into a new phase. Biden also sought to downplay expectations for next Saturday's Nevada caucuses, telling reporters that he did not need to win.

In the interview, the former vice president seized on reports that Sanders' supporters insulted and made online threats against leaders of an influential union that declined to endorse any of the eight candidates still in the Democratic race.

"He may not be responsible for it, but he has some accountability," Biden charged. He continued: "If any of my supporters did that, I'd disown them ... flat disown them."

The Sanders campaign did not immediately respond to a request for comment about Biden's assertion. But Thursday in an interview with PBS, Sanders distanced himself from such behavior. "Anybody making personal attacks against anybody else in my name is not part of our movement," Sanders said, denouncing such behavior in all campaigns.

Earlier Saturday, the fiery progressive senator went on the offensive against his moderate competitors for accepting campaign cash from billionaires, although he declined to go after his opponents by name.

"Democracy is not candidates going to the homes of billionaires raising money," Sanders charged during a rally at a suburban Las Vegas high school.

Both Biden and Pete Buttigieg have aggressively courted wealthy donors over the past year. Buttigieg met with donors behind closed doors in Seattle at roughly the same time Sanders made the comments.

It was a familiar line of attack in a relatively unfamiliar setting as the 2020 primary contest descended upon Nevada for a weekend of frenzied campaigning, colored by mobile campaign billboards cruising the Las Vegas strip and a diverse set of voters weighing in for the first time.

While the state's formal presidential caucuses are still a week away, Democrats opened the first of four days of early voting across more than 80 locations. State party officials at some sites across Nevada were overwhelmed by long lines.

In northern Nevada's Washoe County, a line of more than 300 people snaked through aisles of book shelves at a public library as another 100 queued up at the county party's headquarters. Dozens left without voting.

A spokeswoman for the Nevada Democrats, Molly Forgey, downplayed concerns related to the large early turnout as the political world anxiously watched from afar less than two weeks after Iowa's presidential caucuses turned disastrous.

"We are happy to see the number of energized Democrats participating in our first ever early voting period," Forgey said, noting that early voters have four days to participate. "Our volunteers and staff are working to make every site runs as efficiently as possible and to ensure every voter gets to make their voice heard."

Early votes cast on paper ballots will be added to in-person caucus votes made on Feb. 22, when Democrats will attend about 2,000 precinct meetings around the state. The Nevada State Democratic Party abandoned its plans to use an app like the one that caused trouble in Iowa and has scrambled to come up with a new system to tabulate results.

Amid heightened concern over the process, several candidates were making urgent get-out-the-vote pushes with rallies and town halls ahead of a fundraising gala for the Las Vegas-based Clark County Democratic Party to feature a half-dozen White House hopefuls.

Biden, looking to Nevada's diverse electorate to help revive his campaign after weak finishes in Iowa and New Hampshire, seized on President Donald Trump's hard-line policy and incendiary rhetoric on immigration as he courted voters.

"Everybody knows how Donald Trump is. We gotta let him know who we are," Biden said, drawing a roar from about 100 campaign volunteers gathered at a Las Vegas middle school gymnasium for a Latino organizing event.

Biden thanked the volunteers, emphasized the importance of the Latino vote and touted his relationships with unions. He later told reporters that he didn't need to win Nevada's caucuses to mount a comeback.

"I just have to do well," the former vice president said when asked what he needs out of the state. Asked whether he has to win, he replied, "No, I don't think I have to, but I think we have a shot at winning."

Former Sen. Harry Reid, an icon in Nevada's Democratic politics, told reporters that "people should not be counting Joe Biden out of the race yet," but also offered warm words for Sanders' candidacy. When asked he downplayed concerns from some Democrats that Sanders might hurt other candidates should he become the nominee.

"I care a great deal about Bernie Sanders. And he has gotten where he has by having people support him," said the 80-year-old Reid. "And so I'm not going to be critical of Bernie Sanders."

Elizabeth Warren, meanwhile, also reeling after a weak performance last week in New Hampshire, looked to Nevada's women for momentum.

The Massachusetts senator pitched her universal childcare plan as she addressed about 30 people, mostly women, at a downtown Las Vegas reggae and cocktail bar. After being introduced by actress Yvette Nicole Brown, Warren said her childcare plan would be paid for by a wealth tax of 2 cents on every dollar for fortunes of more than $50 million.

"It's good for our babies," Warren said. "Think about what it means for every mama. Every mama who can now finish her education, even if she's just had a baby. Every mama and every daddy who could take a job."

Mike Bloomberg, who isn't competing in Nevada as part of a strategy to skip the first four states voting for a nominee, was on the cusp of qualifying for Wednesday's presidential debate in La Vegas. The billionaire businessman and former New York mayor has increasingly become a target of the Democratic Party's far-left wing as national polls show suggest he is on the rise.

Both Warren and Sanders criticized the role of big money in politics and billionaires seeking the presidency. Bloomberg and Tom Steyer are in that category.

"Democracy is not billionaires spending hundreds of millions of dollars trying to get elected. Democracy is when working people stand up, fight for justice," Sanders declared.

The campaign of Bloomberg, who campaigned Saturday in Virginia, announced the opening of seven new campaign offices in Florida, bringing the total to 10. The former New York mayor has more than 2,000 paid staff spread out across the nation and has already spent over $300 million on TV, radio and digital advertising, according to the ad tracking firm Advertising Analytics.