Dems' new fear: Sanders revolt could upend Democratic convention

What's more, many Democrats fear that if Sanders does not rein in his supporters, the same ugly scene that occurred in Las Vegas last weekend could replicate itself in the Democratic National Convention in Philadelphia.

"He should get things under control," Boxer said of Sanders, saying it was worse than the vitriol during the Bush-Gore 2000 recount. "We're in a race that is very critical. We have to be united. He knows that. I have in fact, called him a couple times, left a couple messages. I'm hopeful he can get control of this."

Sen. Dianne Feinstein of California said "I do" when asked if Sanders should drop out of the race after voting concludes on June 7, giving Clinton a chance to "pivot" to the general election ahead of the July convention.

"I think it would be most regretful if there becomes a schism," Feinstein said. "That's what Donald Trump should want: a schism in our party. ... It's the responsibility particularly of Sen. Sanders to see that that doesn't happen."

On Tuesday, Senate Minority Leader Harry Reid said he had a "long conversation" with Sanders to lay out what happened in Nevada.

"He said that he condemns that. I'm confident he does," Reid told reporters. "This is a test of leadership."

Reid declined to comment when asked if he was worried that Sanders' backers could upend the national convention this summer.

But Sanders' statement Tuesday was defiant, saying that the Democratic Party "has a choice: It can open its doors and welcome into the party" his backers or "maintain its status quo."

"At (the Nevada) convention, the Democratic leadership used its power to prevent a fair and transparent process from taking place," said Sanders, adding that there have been "zero reports" of violence during his massive rallies across the country.

Asked to respond Tuesday afternoon, Reid was angry, telling CNN it a "silly statement" that "someone else prepared for him."

"Bernie should say something -- not have some silly statement," Reid said. "Bernie is better than that. ... I'm surprised by his statement. I thought he was going to do something different."

Sanders officials say that the Democratic Party should embrace the senator's supporters, not repel them. While they say they don't condone the behavior of some of their supporters at the Nevada convention, they blame leaders of the Nevada Democratic Party for shutting out Sanders' backers, prompting the chaos.

But new audio obtained by CNN shows a senior Sanders aide -- on the eve of the Nevada convention -- encouraging the senator's supporters try to "take it over," apparently referring to the event, change party rules and continue the "revolution" that Sanders has long campaigned on.

"This is your state," Joan Kato, the national delegates director, told Sanders supporters at a meeting to prepare for the convention. "This is your party. This is your opportunity to take it over and for you guys to have an influence that will last way beyond the campaign. And I think that's what the political revolution is all about."

In a meeting last week at the Rumor Boutique Hotel, she told Sanders supporters, "You should not leave."

"I'm going to repeat that, unless you are told by someone from the campaign ... that you can leave, you should not leave."

The Sanders campaign hasn't responded to a request for comment.

After Sanders supporters thought the convention was being shut down prematurely, loud shouting ensued and there were reports of chairs being hurled. The phone number and address of the chairwoman of the Nevada Democratic Party, Roberta Lange, was posted on social media -- prompting a flood of more than 1,000 calls, angry voicemails, text messages and even death threats.

"This is a citizen of the United States of America and I just wanted to let you know that I think people like you should be hung in a public execution to show this world that we won't stand for this sort of corruption," an unidentified male caller said on the message, provided to CNN and other news outlets. "I don't know what kind of money they are paying to you, but I don't know how you sleep at night. You are a sick, twisted piece of s--- and I hope you burn for this! .... You cowardless b---, running off the stage! I hope people find you."

One text message read: "We know where you live... where your kids go to school/grandkids. We have everything on you."

In an interview with CNN's Brooke Baldwin Tuesday, Lange called on Sanders to publicly apologize.

"I've not received an apology," Lange said. "I've not received anything from the campaign. I haven't seen anything that says this should stop. And it's going to continue unless people are made to feel like this isn't ok. This isn't behavior we should have."

On Tuesday, the Nevada Democratic Party sent a formal complaint to the Democratic National Committee, saying Sanders backers and campaign officials "actively incited disruption and violence" at the convention.

Sanders campaign manager Jeff Weaver said on CNN's "New Day" Tuesday that "people who are supporting the senator should act in a civil way."

"They should obviously fight within the context, and by fight, I mean contest if there is a convention, they should be there, they should present their case, and then they should let the votes fall where they may," Weaver said, adding there should be no "threats of violence."

But he also took aim at Democratic leaders in Nevada, saying the "state party has a lot of problems," is run "poorly" and the system in the Silver State is done "very undemocratically" and is "dysfunctional."

"There seems to be an unwillingness on the party of the Nevada Democratic Party to bring in all of the new people that Bernie Sanders has brought into the process," Weaver said.

On Monday evening, Reid -- who has ruled the Nevada state party for years -- blamed Sanders backers for inciting the bedlam that ensued at the convention.

"I've been dealing with Nevada state conventions for 50 years: To say I was disappointed was an understatement," Reid told CNN Monday. "I hold his people accountable, and I'm sure if Bernie found out about it, he would not accept what happened there."

With Sanders warning that he plans to take his campaign to the July convention in Philadelphia, even if he's trailing Clinton in pledged delegates, Democrats are growing increasingly fearful that what happened in Nevada could be repeated just as the party is struggling to unite after a spirited primary.

Senate Majority Whip Dick Durbin of Illinois said "of course" he's concerned that the same tactics would be replicated in Philadelphia.

"We saw what happened at the Trump rallies, which broke into violence, people punching one another. I don't want to see that happen at the Democratic Party," Durbin said in an interview in the Capitol. "I call on Bernie to say to his supporters: be fervent, be committed but be sensible. Don't engage in any violence."

Top Democrats say that it is incumbent on Sanders to bring his supporters in the fold -- or risk electing Trump.

Sen. Jeanne Shaheen, a New Hampshire Democrat who backs Clinton, said she has never before dealt with more aggressive supporters than Sanders' voters.

"It's been interesting to me because I've never experienced that before and I've been involved in every presidential campaign since 1976," Shaheen said. "We've had lots of people who have supported different candidates, and I've never seen that kind of behavior before."

Shaheen recalled an event days before the New Hampshire primary in February when Sanders supporters were "very aggressive," "heckling me and others as we spoke."

"That has never happened before," Shaheen said.

The senator added: "In this campaign, (Sanders) has gotten a lot of people engaged, he should be able to go through the primaries as he's committed to do -- Hillary Clinton did that in 2008," Shaheen said. "Hopefully, once the nomination is done, then he will endorse the nominee."