Sen. Kamala Harris, who clashed with Joe Biden on the debate stage earlier in the Democratic primary race, endorsed the former vice president on Sunday.

The California Democrat said in a Twitter post that Biden "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."

"I have decided that I am, with great enthusiasm, going to endorse Joe Biden for president of the United States," Harris said in a video directed at her supporters, which was posted with the tweet. "I believe in Joe. I really believe in him, and I have known him for a long time. One of the things that 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."

Harris has been floated as a strong running mate for Biden, who told reporters in December that "of course" he would consider her for vice president.

"Sen. Harris has the capacity to be anything she wants to be. I mean it sincerely," Biden said. "She is solid. She can be president someday herself. She can be the vice president. She can go on to be a Supreme Court justice. She can be an attorney general. I mean, she has enormous capability."

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In June during the first Democratic debate, the former California attorney general went after Biden, who was considered the front-runner for most of 2019, on his civil rights record.

Harris challenged Biden over remarks he made at a fundraiser in which he touted his past successes working with Republicans to get legislation passed, citing his ability to work with segregationist Sens. James Eastland and Herman Talmadge.

"It was hurtful to hear you talk about the reputations of two United States senators who built their reputations and careers on segregation of race in this country," Harris, who is African-American, told Biden.

She went on to criticize his opposition to school busing in the 1970s, telling the story of a girl in California who was part of just the second integrated class in her school.

"That little girl is me," Harris said.

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Biden fired back, calling her comments a "mischaracterization" of his positions and saying, "I don't praise racists."

That debate performance in Miami helped Harris take off in national polls. Multiple surveys found her in second place after that debate, including one from Quinnipiac University that found her just 2 percentage points behind Biden.

But that bumped was short-lived. Though Harris was consistently one of the top-five performing candidates in national polls, along with Biden, Sanders, Sen. Elizabeth Warren and former South Bend, Indiana, Mayor Pete Buttigieg, she never returned to the level of support she had in July.

Harris dropped out of the race in December, citing a lack of money. When she left, the number of candidates remaining in the field was still in the double digits. Now, only Biden, Sen. Bernie Sanders of Vermont and Rep. Tulsi Gabbard of Hawaii remain. Gabbard, with only two delegates under her belt after Super Tuesday, does not appear to have a viable path to the nomination.

When asked about Harris's endorsement of Biden on ABC News' "This Week," Sanders said it was "no secret" that his campaign "was not going to get the support of most elected leaders. Not most governors, not most senators."

Sanders, a self-described democratic socialist, said he is taking on the party establishment, which he claimed forced out Buttigieg and Sen. Amy Klobuchar – ignoring their low delegate totals and poor polling numbers – because "the establishment wanted was to make sure that people coalesced around Biden and try to defeat me."

In his response to Harris' endorsement of Biden, Sanders announced that prominent African-American civil rights leader Jesse Jackson would declare his support for Sanders at an event in Michigan later Sunday.

Buttigieg and Klobuchar exited the race after disappointing performances in the South Carolina primary. Warren and billionaire Mike Bloomberg followed suit after failing to gain ground on Super Tuesday, when a third of the pledged delegates needed to secure the nomination was at stake.

Buttigieg, Klobuchar and Bloomberg endorsed Biden after dropping out. Other former candidates who have thrown their support behind Biden include Rep. Tom Ryan of Ohio, former Massachusetts Gov. Deval Patrick and former Reps. Beto O'Rourke of Texas and John Delaney of Maryland.

With the race now a contest between Biden and Sanders to see which of them will take on President Donald Trump in November, it is all but certain that the next president will be a white man in his 70s.

In a written statement endorsing Biden, Harris expressed disappointment that there were no viable female candidates remaining.

"Like many women, I watched with sadness as women exited the race one by one. Four years after our nominee, the first woman to win the nomination of a major party, received 3 million more votes than Donald Trump but still lost, we find ourselves without any woman on a path to be the Democratic nominee for president," Harris said.

"But we must rise to unite the party and country behind a candidate who reflects the decency and dignity of the American people and who can ultimately defeat Donald Trump."

Contributing: Christal Hayes and Savannah Behrmann

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