St. Paul, Minnesota (CNN) Bernie Sanders has spent his entire campaign saying this day would come.

Now, it's here.

After more than a year of angling and long periods of indecision, the leaders of the moderate wing of the Democratic Party are rapidly coming together to lift and fortify former Vice President Joe Biden ahead of Super Tuesday . The dramatic coalescing around Biden all came over two days that set the party's presidential race on a collision course between Sanders' political revolution and Biden's bid to revive former President Barack Obama's legacy.

The Super Tuesday contests, with about a third of the delegates to the national convention on the line, could decide more than the trajectory of this primary. A run of victories for Sanders in states like California, Texas and Minnesota have the potential to fundamentally alter the identity of a party he has for decades sought to remake according to his own vision. But if Biden can pull together undecided voters, especially suburban moderates, Sanders' position would be dramatically weakened -- and his campaign's early promise put in doubt.

That dynamic is comfortable territory for Sanders, who on Monday responded matter-of-factly to the rush of support for Biden. He has been predicting a fight with the party establishment would happen, in one form or another, for months. As he jumped up in the polls at the end of last year, and then won in New Hampshire and Nevada , Sanders has delighted in poking at party leaders' increasingly vocal anxieties over his rise. After inviting Buttigieg and Klobuchar supporters to join his campaign -- "The door is open," he said, "come on in!" -- Sanders at his Super Tuesday eve rally in Minnesota, turned his attention back to the "political establishment."

"When they look at rallies like this in St. Paul and say, 'What's going on here?'," Sanders said, before asking his supporters to "imagine a Democratic Party in which working people and young people finally have a voice."

Speaking to reporters in Salt Lake City earlier in the day, Sanders touted his own new endorsements: from the progressive group Democracy for America and The Nation, a liberal magazine. He also name-checked other high-profile backers, including Minnesota Rep. Ilhan Omar, New York Rep. Alexandria Ocasio-Cortez and California Rep. Ro Khanna, a campaign co-chair.

"I'm proud of the grassroots organizations that we have. Look, we are taking on the establishment. And I fully understand, no great surprise to me that establishment politicians are not going to endorse us," Sanders said when asked about Biden's recent haul. "The establishment will rally around establishment candidates. That's the simple reality."

Moderate unity in Texas

The depths of the Democratic establishment's determination to trip up Sanders was on display in Dallas on Monday night, when bitter debate stage foes Sen. Amy Klobuchar and former South Bend, Indiana, Mayor Pete Buttigieg , along with former Texas Rep. Beto O'Rourke , all publicly announced their support over the course of a few hours.

The barrage of endorsements, from state lawmakers to a pair of candidates who dropped out of the race in the last 24 hours, has created a united front determined to boost Biden and, just as importantly, block Sanders from running away with party's presidential nomination. If Biden falters, the anti-Sanders crowd will be thrown into a new and heightened stage of panic, with no one -- save for late-entering former New York City Mayor Michael Bloomberg -- left in the field with the resources or inclination to square off against the Vermont senator and his call for political revolution.

Biden welcomed his former foes Buttigieg, Klobuchar and O'Rourke with warm words as he tried to demonstrate to Democratic voters across the country that he -- not Bloomberg -- was the consensus choice to take on Sanders.

"I don't think I've ever done this before, but he reminds me of my son, Beau," Biden said of Buttigieg, referring to the son that died of brain cancer as the two appeared together for the first time.

"And folks, I wasn't joking: Amy won all of the debates," he said of Klobuchar later at a show-of-force rally in Dallas.

Adding their former supporters could help Biden expand a playing field Tuesday that his campaign had previously worried would be limited to racking up delegates in largely African American congressional districts in the south, but that now looks much broader.

Biden's closer in Dallas was O'Rourke, who electrified Texas Democrats during his 2018 Senate run.

"We need somebody who can beat Donald Trump. The man in the White House today poses an existential threat to this country, to our democracy, to free and fair elections; and we need somebody who can beat him. And in Joe Biden we have that man," O'Rourke said.

While Biden's rallies were infused with an enthusiasm that had eluded him until just days ago, endorsements continued to rain in from afar. In Nevada, former Sen. Majority Leader Harry Reid, a party elder respected across its ideological chasm, also backed Biden, calling him the "candidate who can assemble the largest, most diverse coalition possible to defeat Trump and lead our country following the trauma of Trump's presidency."

Split between Warren and Sanders

Warren shakes hands with supporters after speaking during a townhall at Discovery Green in Houston, Texas, on February 29, 2020. (Photo by Mark Felix / AFP) (Photo by MARK FELIX/AFP /AFP via Getty Images)

Progressives could face a critical coalition-building question of their own after the votes are counted on Tuesday.

Massachusetts Sen. Elizabeth Warren , despite failing to finish in the top-two of any of the first four nominating contests, remains determined to push on, perhaps all the way to this summer's convention in Milwaukee.

In a memo published Sunday morning, Warren campaign manager Roger Lau celebrated her February fundraising -- nearly $30 million, he wrote -- and doubled down on a strategy that depends on collecting delegates from Tuesday, right on through to late April and beyond.

"Our internal projections continue to show Elizabeth winning delegates in nearly every state in play on Super Tuesday, and in a strong position to earn a sizable delegate haul coming out of the night," Lau wrote. "But as the dust settles after March 3, the reality of this race will be clear: no candidate will likely have a path to the majority of delegates needed to win an outright claim to the Democratic nomination."

The Warren campaign believes it can emerge from the chaos -- potentially with the help of superdelegates -- and unite moderates and progressives.

"In the road to the nomination, the Wisconsin primary is halftime," Lau wrote, "and the convention in Milwaukee is the final play."

It is a bold and potentially divisive play -- one that is as likely to alienate both sides of the party's ideological divide as bring them together around Warren. There is also some disagreement among progressives over what effect Warren's departure would have on the balance of the race, with some discounting the suggestion her support would flock to Sanders.

But that cross-conversation has largely been subsumed over recent days by renewed worries over what appears to be an increasingly bitter split between Warren and Sanders and the damage it could do to a movement that largely reveres both.

Alexandra Rojas, executive director of Justice Democrats, in a statement Monday night called on Warren stop her swipes at Sanders and pledge to back him in the event he arrives in Milwaukee with a plurality of delegates.

"I hope she stops attacking Senator Sanders and publicly commits to give her delegates to him if he has more votes to ensure a progressive wins the nomination. I'd say the same to Bernie," Rojas said. "Pursuing the nomination through a contested convention without accumulating the most delegates would be harmful for our movement, our party, and the policies she's spent her life fighting for."

Some are demanding she drop out and endorse Sanders; others, including groups like the Working Families Party, cheered Buttigieg's withdrawal from the race on Sunday night, noting in a fundraising email that Warren is "the second choice for a LOT of Pete Buttigieg supporters."

The split between Sanders and Warren has become more pronounced over the last few weeks. Warren has ratcheted up her criticisms of Sanders, taking an eyebrow-raising swipe at her fellow progressive on Saturday night, after the South Carolina results came in.

"This crisis demands more than a senator who has good ideas, but whose 30-year track record shows he consistently calls for things he fails to get done, and consistently opposes things he nevertheless fails to stop," she said at a rally in Houston.

Asked on Monday whether Warren should leave the race, Sanders' deputy campaign manager Ari Rabin-Havt demurred.

"I think campaigns should always be able to make their own choices," he told reporters. "I wouldn't want them making choices for our campaign."