Washington (AFP) – Senator Kamala Harris endorsed Joe Biden for the Democratic presidential nomination Sunday, while his chief rival Bernie Sanders won the backing of civil rights leader Jesse Jackson as the rival candidates competed for African American support.

Harris said she was coming out for Biden because she believes the former vice president can best unify the country going into crucial November US elections against Donald Trump.

“I have decided that I am with great enthusiasm going to endorse Joe Biden for president of the United States,” she said in a videotaped statement posted on Twitter.

Biden later responded, also on Twitter, saying to Harris, “You’ve spent your whole career fighting for folks who’ve been written off and left behind — and no small part of that alongside Beau. From our family: thank you.”

Biden’s late son Beau worked closely with Harris when he was attorney general of Delaware and she held the same position in California.

A onetime rival of Joe Biden’s, Harris made waves early in the Democratic race by chastising him in a televised debate in June 2019 over his warm words for past segregationist senators and opposition to busing to integrate US schools in the 1970s.

But many African American leaders have since swung behind Biden, helping to resurrect his once flagging campaign with decisive victories in South Carolina and a string of Super Tuesday contests.

“I believe in Joe, I really believe in him and I have known him for a long time,” Harris said.

She follows former candidates Pete Buttigieg, Amy Klobuchar and Beto O’Rourke in endorsing Biden.

Jackson, in a statement posted by the Sanders campaign, noted that the “black firewall” of support for Biden had changed the dynamics of the race, but he questioned whether moderate policies would benefit African Americans.

“A people far behind cannot catch up choosing the most moderate path,” he said.

“The most progressive social and economic path gives us the best chance to catch up and Senator Bernie Sanders represents the most progressive path. That’s why I choose to endorse him today.”

Sanders, who has had trouble attracting black support, touted the endorsement on Sunday television talk shows, calling Jackson “one of the great civil rights leaders in the modern history of this country.”

“He changed American politics with the concept of the Rainbow Coalition — getting the blacks and whites and Latinos together in ’84 and ’88,” Sanders said on ABC’s “This Week.”

“He’s been a leader in helping to transform this country, an aide to Dr. Martin Luther King Jr., so we’re proud.”