Former Vice President Joe Biden can add another former rival to his campaign's endorsement tally.

On Sunday morning, California Sen. Kamala Harris threw her support "with great enthusiasm" behind the Democratic frontrunner.

"I believe in Joe. I really believe in him, and I have known him for a long time," Harris said in a Twitter video.

Sen. Kamala Harris. (Tom Williams/CQ-Roll Call, Inc via Getty Images)

"One of the things we need right now is we need a leader who really does care about the people, and who can, therefore, unify the people. And I believe Joe can do that," she continued. "I am supporting Joe because I believe he is a man who has lived his life with great dignity. He is a public servant who has always worked for the best of who we are as a nation. And we need that right now."

.@JoeBiden has served our country with dignity and we need him now more than ever. I will do everything in my power to help elect him the next President of the United States. pic.twitter.com/DbB2fGWpaa — Kamala Harris (@KamalaHarris) March 8, 2020

Harris joins Sen. Amy Klobuchar of Minnesota, from South Bend Mayor Pete Buttigieg and former Rep. Beto O'Rourke of Texas on the list of former 2020 Democratic presidential candidates who have dropped out and endorsed Biden.

Her endorsement is notable as she was among Biden's fiercest critics in the early debates, attacking him for opposing federally mandated busing in the 1970s and for comments he made about working with “civility” alongside two Southern segregationist senators in the '70s and '80s.

At a debate last summer, Harris told Biden it was “personal” and “hurtful to hear you talk about the reputations of two United States senators who built their reputations and career on segregation of race in this country.” (She dropped out of the race at the end of last year.)

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Her endorsement also lands two days before the next series of primaries, which on March 10 will offer Biden and his main rival, Sen. Bernie Sanders of Vermont, the opportunity to battle it out in Michigan, Missouri, Washington state, Mississippi, Idaho and North Dakota. A week ago on Super Tuesday, Biden surprised observers by winning states he wasn't expected to and building up a small but significant delegate lead.

Harris also appeared to be eyeing the upcoming elections.

"Come and hang out," she said in her Sunday video. "We're going to be in Detroit Monday night."

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