BERNIE SANDERS HAS endorsed his former rival in the US presidential campaign Joe Biden this evening.

The backing is a crucial development for Biden, who must bridge the Democratic Party’s ideological divide to unify voters against Republican president Donald Trump.

Biden and Sanders, a leading progressive, clashed throughout the primary over policy issues such as the “Medicare for All” universal health care plan.

“I am asking all Americans, I’m asking every Democrat, I’m asking every independent, I’m asking a lot of Republicans, to come together in this campaign to support your candidacy, which I endorse,” Sanders said.

The endorsement stands in contrast to the extended 2016 fight between Sanders and Hillary Clinton, who became the nominee that year.

He only endorsed her at the end of a drawn-out nominating fight and amid a bitter fight over the Democratic platform that extended to the summer convention.

Appearing in a split screen with  Biden, Sanders said there is “no great secret out there that you and I have our differences”.

But he cited ongoing work between the two camps on several policy matters as a reason for the endorsement.

He added the biggest priority was defeating Trump in November.

“We’ve got to make Trump a one-term president,” Sanders said.

“I will do all that I can to make that happen.”

- With reporting by Michelle Hennessy