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Biden joined in Texas by rivals-turned-endorsers Buttigieg, Klobuchar and O'Rourke

The former vice president picked up the support ahead of crucial primaries on Super Tuesday.

Riding a wave of big endorsements, Joe Biden appeared on stage with former rivals Amy Klobuchar and Beto O'Rourke on Monday night and presented his emerging two-person race with Bernie Sanders as a battle for the soul of the Democratic Party one day before a critical swath of contests that will shape the race.

Pete Buttigieg flew from South Bend, Indiana, to Dallas to endorse Biden before his rally but returned home and did not join the former vice president at the event.

At the rally, Biden told cheering supporters that Super Tuesday voters are "going to determine what this party stands for, what we believe and what we're going to get done" — and took a series of swipes at Sanders.

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"If Democrats want a nominee who will build on Obamacare, not scrap it; take on the NRA and gun manufacturers, protect our children; who'll stand up for the middle class, not raise their taxes and make promises that can't be kept, then join us," Biden said. "If Democrats want a nominee who’s a Democrat, a lifelong Democrat, a proud Democrat, a lifelong Democrat, then join us. We can either win big or lose big, that’s the choice."

Texas votes with 13 other states on Super Tuesday, a day when one-third of delegates to the party's convention this summer will be up for grabs.

A running theme in the remarks of Buttigieg, Klobuchar and O'Rourke was that Biden is the party's best chance at victory and offers a decent and caring alternative to President Donald Trump.

"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," O'Rourke said. "In Joe Biden, we have that man."

Buttigieg said Biden would "bring back dignity to the White House" if elected president and "change the toxic and divisive nature of our politics right now."

"He is somebody of such extraordinary grace and kindness and empathy," the former mayor of South Bend, Indiana, said.

In a lighter moment at the rally, Klobuchar mentioned being onstage for the debates, to which Biden leaned over into the microphone and said, "all of which you won."

Klobuchar also appeared to take a veiled dig at Sanders.

"It is time for a president who represents all of America, including people at the middle of this country, at a time when we see people in extremes that are trying to drown out people," she said.

Speaking to reporters in Salt Lake City on Monday, Sanders addressed the consolidation of party elites behind Biden, calling it "a massive effort trying to stop Bernie Sanders."

"The corporate establishment is coming together. The political establishment is coming together and they will do everything. They are really getting nervous that working people are standing up … We are winning working class voters, by big numbers," Sanders said. "So it doesn't surprise me. Why would I be surprised that establishment politicians are coming together?"