The former Democratic presidential candidate Beto O’Rourke has endorsed Joe Biden ahead of Super Tuesday, despite previously criticising him as a “return to the past”.

On Monday evening, Mr O’Rourke, who withdrew his own candidacy in November, told a campaign rally in Dallas, Texas: "Tomorrow, March 3, 2020, I will be casting my ballot for Joe Biden."

The former Representative for Texas said: "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.”

He added that Joe Biden was the “antithesis of Donald Trump” and could defeat the incumbent president in an election.

Mr O’Rourke’s support for Mr Biden comes just nine months after he affirmed on MSNBC that the former vice president represented a “return to the past”.

"And that cannot be who we are going forward. We've got to be bigger. We've got to be bolder. We have to set a much higher mark and be relentless in pursuing that,” Mr O’Rourke said.

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On a good night for the Democratic presidential candidate, Amy Klobuchar and Pete Buttigieg, who both recently dropped out of the race, also expressed their support for him.

Mr Buttigieg said on Monday evening that the party needed to “change the toxic and divisive nature” of the country’s politics, adding that Mr Biden was best-placed to achieve this.

These high-profile endorsements are part of efforts from the moderate wing of the Democratic Party to rally behind an alternative to Bernie Sanders, who so far won the highest number of delegates.

They came just hours before Super Tuesday, the day when 14 states – including California and Texas, the two most populated states - and one US territory vote.

Over 1,300 delegates are allocated on a single day of voting on Tuesday, meaning that one candidate could effectively gain an unassailable lead in the race.

To win the Democratic nomination, a candidates needs 1,991 out of 3,979 pledged delegates.

Of those left in the contest, Mr Sanders has so far received the support of 60 delegates, with Mr Biden trailing on 54 and Elizabeth Warren on 8.