Bernie Sanders’ surge in national polls and success in the early-voting states has Democratic Party elders increasingly concerned about the self-proclaimed democratic socialist’s potential to become their nominee -- as he heads into this weekend's Nevada caucuses with a massive lead and aiming to cement his front-runner status.

Establishment Democrats inside and outside of Washington have sounded the alarms over Sanders’ success, warning that his nomination would pave the way for President Trump's re-election and potentially hurt Democrats' chances of maintaining the majority in the House and taking the majority in the Senate.

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Most recently, former Senate Majority Leader Harry Reid, D-Nev., this week appeared to nudge the center-left presidential candidates to eventually coalesce around one candidate who can win enough delegates to secure the nomination.

“A lot of this will work its way out,” he told The Washington Post. “A lot of people in the race still, but they’ll be dropping off quick because the money is running out. So I think you’re going to have the field winnowing pretty quickly.”

He added: “And you have most of the people who are not Bernie Sanders, are people who are moderates, and maybe they’ll work something out to get together and try to find that one person who can come up with the number of delegates. Maybe that’s one way to do it.”

But right now, the non-Sanders candidates are showing no inclination to make way for a consensus pick -- while still warning about the threat that Sanders will win if the field remains this large.

In a memo from former New York City Mayor Mike Bloomberg’s campaign ahead of Wednesday’s debate, they warned that Sanders would be nearly unstoppable unless other moderate candidates drop out before Super Tuesday.

“As the race stands today, Sanders is poised to leave Super Tuesday with an over-400 delegate lead versus his next closest competitor [Bloomberg]—a likely insurmountable advantage,” the memo said.

The Bloomberg campaign memo emphasized that “if Biden, Buttigieg, and Klobuchar remain in the race despite having no path to appreciably collecting delegates on Super Tuesday (and beyond), they will propel Sanders to a seemingly insurmountable delegate lead by siphoning votes away from [Bloomberg].”

Former South Bend Mayor Pete Buttigieg, though, said maybe Bloomberg should “step aside.”

“If he thinks there’s gotta be one alternative to Bernie Sanders, I suppose we could find common ground on that. Maybe he should step aside and the person who has the most delegates move on,” Buttigieg told Fox News after the debate Wednesday.

Reid’s comments come after Sanders made clear at this week's debate that he thinks the candidate with the most delegates—not necessarily the majority of delegates—at the end of the primary calendar should win the nomination. The other candidates on stage did not agree with that assertion -- seemingly entertaining the scenario of a contested convention where "superdelegate" party insiders could play a role.

“If [Sanders] is the nominee, we lose,” one Democrat told Fox News earlier this month, with two other vulnerable congressional Democrats saying a Sanders nomination would almost certainly cede their states to Trump and even have the potential to hurt their down-ballot races for the House and Senate.

“Elected officials across the country understand there will be down-ballot carnage to the Democratic Party if we elect the wrong person,” Rep. Cedric Richmond of Louisiana, a Biden campaign co-chair, stressed during a conference call with reporters. “If Bernie Sanders were atop of the ticket, we would be in jeopardy of losing the House, we would not win the Senate back.”

Outside of Washington, former top Democrats are also expressing mounting concern over Sanders’ momentum, while plotting alternative options.

Former Secretary of State John Kerry, who endorsed former Vice President Joe Biden in December, reportedly was overheard in a hotel restaurant warning of the very real “possibility of Bernie Sanders taking down the Democratic Party—down whole,” according to an NBC News report that said he also floated the possibility of running himself.

Kerry fired back in a profanity-laced tweet, maintaining that he would not launch a presidential bid and that his support remains with Biden, but did not deny blasting Sanders.

A November report also claimed that former President Barack Obama once stated privately that he would speak out against Sanders if it appeared that he was pulling ahead of the pack. An Obama spokesperson, however, reportedly noted that the former president has stated that he would get behind the Democratic nominee no matter who it is.

This week, Sanders said he was “extremely confident” that he will have the support of Obama.

“I’m not going to tell you that he and I are best friends, but we are friends,” Sanders told CNN on Thursday. “I have talked to him on and off for the last many years, was sitting down alone with him in the Oval Office on more than one occasion, I have talked to him on the telephone every now and then.”

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“He is an icon, clearly, in the Democratic Party and I have absolute confidence that he will play a vigorous, vigorous role—I think he had said this in the campaign. And, we need him. No question about it. We need him,” he continued. “And if I win, I’m sure he will be there at my side. If somebody else wins, he will be there at their side.”

The debate moment concerning delegates was illuminating, and pointed to a contentious primary contest ahead that could potentially last through the convention.

During Wednesday debate, Democratic candidates were asked whether the person with the most delegates at the end of the primary season should be the nominee, even if they were short of a majority.

Every Democratic presidential hopeful said the party rules at the Democratic National Convention, slated to take place in July, “should be followed”—except for Sanders.

“Well, the process includes 500 superdelegates on the second ballot, so I think the will of the people should prevail. Yes,” Sanders said. “The person with the most votes should become the nominee.”

After the first two contests—the Iowa caucuses and the New Hampshire primary last week—Buttigieg leads in the delegate count with 22, followed by Sanders with 21, Sen. Elizabeth Warren, D-Mass., with eight, Sen. Amy Klobuchar, D-Minn., with seven and former Vice President Joe Biden with six. A total of 1,991 delegates are needed to secure the Democratic nomination.

Meanwhile, one Democratic congressional aide close to House Democratic leadership downplayed concerns about Sanders completely, telling Fox News on Friday: "He won't win."

Fox News' Paul Steinhauser, Kelly Phares, Marisa Schultz and Tyler Olson contributed to this report.