WASHINGTON — Presumptive Democratic nominee Joe Biden on Tuesday tapped Senator Kamala Harris of California to be his running mate, elevating the first Black woman in US history to that role ahead of next week’s party convention.

Biden announced the long-awaited decision via Twitter, calling Harris “a fearless fighter for the little guy and one of the country’s finest public servants.” His campaign said the two will deliver remarks together Wednesday in Wilmington, Del.

Harris, the former attorney general of California and the only Black woman in the US Senate, clashed with Biden on the issue of race during her short-lived presidential run last year. But she later shot to the top of his vice presidential list as he vowed to pick a woman and underscored the importance of experience.

Harris, 55, makes for a barrier-breaking pick at a time when many voters are demanding change and equality for Black people amid extensive civil rights protests around the country. She would be the first woman or Black person to become vice president if elected, and Democratic activists have long pushed Biden to pick a woman of color in a nod to the party’s most loyal constituency.

But Harris’s extensive record in law enforcement — formed during the tough-on-crime 1990s — could become a liability for her among Democrats who are pushing for aggressive criminal justice reforms in the wake of George Floyd’s killing. Harris has marched in Floyd protests in Washington and skillfully described activists’ “defund the police” slogan as a reimagining of public safety in America.

Harris beat out several contenders on Biden’s list, including Senator Elizabeth Warren, former Obama administration official Susan Rice, Georgia politician Stacey Abrams, and Florida Representative Val Demings. Biden, who knows the job having served as Barack Obama’s vice president, stressed he wanted a running mate he felt “simpatico” with, as well as someone who was ready to assume the presidency if necessary.

Since joining the Senate in 2017, Harris made a name for herself on the left with her pointed questioning of Trump administration officials in committee hearings, and later, with her presidential run. That run fizzled and she dropped out of the race before the Iowa caucuses despite a strong start that included a kickoff event in Oakland with more than 20,000 fans.

Harris, the child of Indian and Jamaican immigrants, drew headlines and a short-lived polling bump with a blistering debate attack on Biden’s past stance against busing to desegregate schools. Harris said then that she didn’t believe Biden was a “racist,” but that she benefited from a busing program that integrated schools when she was a child. “That little girl was me,” she said during the June 2019 debate exchange in a phrase her campaign quickly pasted over T-shirts. Biden’s wife, Jill Biden, later called that moment “a punch in the gut.”

But Harris repaired her relationship with Biden after dropping out, endorsing him following his Super Tuesday sweep and going to work to raise money and campaign for him virtually during the pandemic. Harris’s friendship with Biden’s late son Beau Biden, who was attorney general of Delaware when she held that post in California, also provides her with a personal connection to the nominee.

The pick marks a watershed moment for Harris, who will now likely be a fixture in the Democratic party for years to come. Biden’s age — at 77 years old he would be the oldest person ever elected president — and ambiguity about whether he would seek a second term make Harris likely to be a top contender for the presidency in four years, should the pair win in 2020.

Harris joins the ticket as polls show Biden with a steady lead over Trump, who has battled low approval ratings over his handling of the coronavirus and race relations. It remains unclear how the Trump campaign, which has struggled to define Biden negatively, will attack Harris. Trump said she would be a “fine choice” when asked about her in late July — an uncharacteristically neutral response from the king of derogatory political nicknames.

The president has sought to stir up anxieties among white voters about recent protests for racial justice and the toppling of Confederate and other statues — calling Biden a secret radical who wants to remake the country. But at the same time, Trump’s campaign has run ads aimed at Black voters reminding them of Biden’s key role in passing a landmark crime bill in 1994 that contributed to rising incarceration rates. The Trump campaign could seize on Harris’s past as a prosecutor and attorney general to make similar arguments aimed at suppressing the Black vote.

Harris is still unknown to more voters than Biden or Trump, with one recent poll showing 79 percent of voters know who she is. Out of the running mate contenders Biden was contemplating, however, she was the second-most well known after Elizabeth Warren.- Boston Globe