Former Vice President Joe Biden will formally endorse Tom Perez for Democratic National Committee chair, three sources confirmed to The Daily Beast. Biden’s official endorsement of Perez is expected to be made in the form of a written statement, and is set to be released by Perez’s campaign this week.

Perez, a civil rights attorney and a Secretary of Labor under President Obama, is locked in a tight race for DNC, leadership with Keith Ellison, the first Muslim-American congressman who has secured the endorsement of several progressive leaders including Bernie Sanders.

Since as recently as last week, Perez had been telling DNC members that he had secured Biden's endorsement. At the site of last weekend's DNC forum in Houston, Texas, Perez was discussing the future of the Democratic Party with a private gathering of DNC members. According to two sources familiar with the exchanges, Perez excitedly said, in an apparent effort to drum up more support from DNC members, that the former vice president had his back. "And that’s why Joe Biden is coming out for me next week,” one DNC member recalled Perez saying.

Biden's endorsement underscores a growing rift within the Democratic Party between establishment-backed figures and those deeply dissatisfied with how the DNC has been run in recent years and who wish to push the party leftward. Many backing Ellison's candidacy say that reports that Perez had the full backing of the Obama White House shows that he represents an old guard out of touch of what needs to be done to win in an uncharted Trump era. Those supporting Perez insist that he is a "progressive who gets things done," a favorite talking point of the former Labor Secretary.

A representative for Biden did not immediately respond to a request for comment on this story.

—Asawin Suebsaeng