Joe Biden named California Sen. Kamala Harris as his running mate on Tuesday to compete on a major party's presidential ticket, a move seen acknowledging the vital role Black voters will play in his bid to defeat President Donald Trump in the November 3 election.

Biden's announcement capped a months-long search for a Democratic partner to campaign for the predidential race.

"I have the great honor to announce that I've picked @KamalaHarris a fearless fighter for the little guy, and one of the country's finest public servants — as my running mate," Biden, 77, wrote on Twitter. "I'm proud now to have her as my partner in this campaign."

The decision, announced in typical 2020 style on social media, was a crucial moment for Biden as he aims to build a broad coalition of voters to oust Trump from the White House.

"Back when Kamala was Attorney General, she worked closely with Beau. I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse. I was proud then, and I'm proud now to have her as my partner in this campaign."

In choosing Harris, Biden is embracing a former rival from the Democratic primary who is familiar with the unique rigor of a national campaign. Harris, the first-term senator, is also one of the party's most prominent figures and quickly became a top contender for the No. 2 spot after her own White House campaign ended.

Harris, who at 55 is two decades Biden's junior, could appeal to women voters, particularly those in the U.S. suburbs who have been leaning away from Trump. The former California attorney general also personifies the diversity seen as key to building enthusiasm for the Democratic ticket.

Taking to Twitter shortly after the announcement, Harris said she was "honored" to now join him as nominee for vice president, and would "do what it takes" to help him win. "@JoeBiden can unify the American people because he's spent his life fighting for us. And as president, he'll build an America that lives up to our ideals," she wrote.

For Harris, being elevated onto a Democratic presidential ticket is the political moment of a lifetime. And if they win, the telegenic but tough Californian becomes the automatic frontrunner in the race for the 2024 or 2028 Democratic nomination.

Biden, who is three years older than Trump, would be the oldest person to take the office, and there is broad speculation that should Biden win, he would serve a single term and groom his deputy to succeed him.

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Trump on Tuesday said he was surprised Biden chose Senator Harris as his running mate because she had been disrespectful to the former vice president during the debates.

Trump said Harris had been "very, very nasty" to Biden during the primaries. "One of the reasons that it surprised me, she was probably nastier than even Pocahontas to Joe Biden. She was very disrespectful to Joe Biden and it's hard to pick somebody that that's disrespectful," he told reporters.

"And that's like a poll," he went on to attack Harris for her role in the bruising confirmation hearings of Supreme Court Justice Brett Kavanaugh, calling her "the meanest, the most horrible, the most disrespectful of anybody in the U.S. Senate."

But Harris, who beat out nearly a dozen other women to become the running mate, has shown she can withstand an onslaught of negativity from a caustic president.

Biden's pick of Harris drew ringing endorsements from other quarters – including from Barack Obama, America's first black commander in chief. "She is more than prepared for the job," tweeted Trump's predecessor. "This is a good day for our country. Now let's go win this thing."

Harris joins Biden in the 2020 race at a moment of unprecedented national crisis. The coronavirus pandemic has claimed the lives of more than 150,000 Americans, far more than the toll experienced in other countries. Business closures and disruptions resulting from the pandemic have caused an economic collapse. Unrest, meanwhile, has emerged across the country as Americans protest racism and police brutality.

Trump's uneven handling of the crises has given Biden an opening, and he enters the fall campaign in strong position against the president. In adding Harris to the ticket, he can point to her relatively centrist record on issues such as health care and her background in law enforcement in the nation's largest state.

Harris' record as California attorney general and district attorney in San Francisco was heavily scrutinized during the Democratic primary and turned off some liberals and younger Black voters who saw her as out of step on issues of systemic racism in the legal system and police brutality. She tried to strike a balance on these issues, declaring herself a "progressive prosecutor" who backs law enforcement reforms.

(With input from AFP, Reuters)

(Cover: Former Vice President Joe Biden (L) and U.S. Senator Kamala Harris take the stage before the start of the second night of the second U.S. 2020 presidential Democratic candidates debate in Detroit, Michigan, U.S., July 31, 2019. /Reuters)