Senator Kamala Harris endorsed Joe Biden on Sunday and said she would "do everything in my power" to help elect him.
Her endorsement comes before the next round of primaries, with six states voting Tuesday, including Michigan and Mississippi.
Vermont Senator Bernie Sanders countered with his own major endorsement, announcing that civil rights icon Jesse Jackson was formally backing him.
Jackson appeared with Sanders during a campaign stop in Grand Rapids, Michigan. He says he chose Sanders after the senator's campaign offered responses on 13 issues Jackson raised — including protecting voting rights, increasing funding for historically black colleges and universities and committing to putting African Americans on the Supreme Court, according to prepared remarks released by the campaign.
In a statement on Biden, Harris said: "There is no one better prepared than Joe to steer our nation through these turbulent times, and restore truth, honor, and decency to the Oval Office."
“He is kind and endlessly caring, and he truly listens to the American people,” her statement added.