WASHINGTON — In naming Kamala Harris as his running mate, Joseph R. Biden Jr. made a groundbreaking decision, picking a woman of color to be vice president and, possibly, a successor in the White House someday. Yet in some ways, Mr. Biden made a conventional choice: elevating a senator who brings generational and coastal balance to the Democratic ticket and shares his center-left politics at a time of progressive change in the party.
Unlike Barack Obama and George W. Bush, who selected veteran Washington hands as their vice presidents, Mr. Biden, 77, is opting for a time-honored model in which running mates are not just governing partners but political understudies of sorts. Pegged as a rising star for a decade, but with less than four years of experience in the Senate — she was 8 years old when Mr. Biden was first elected to the chamber — Ms. Harris, 55, reflects a traditional archetype in an election year that has been anything but normal.
She is also a thoroughly establishment-friendly figure, as is Mr. Biden: Both have hewed closely to their party’s mainstream for years, shifting left with the times but always with an eye on the broader electorate and higher office. He long said he wanted someone “simpatico” with him and, in Ms. Harris, he found that person, at least when it comes to ideology.
Progressive Democrats now find themselves led by two moderates with relatively cautious political instincts, even as activist energy courses through the party and left-wing challengers unseat some incumbents. The mostly young protesters filling the streets of nearly every American city to denounce police brutality and President Trump are represented by two figures who have offered sympathetic words and proposals but whose careers have been shaped by their relationship with law enforcement.
“She’s not of the far left of the party, she’s a former prosecutor,” Janet Napolitano, the former Arizona governor and Homeland Security secretary, said of Ms. Harris. “And when you’re a prosecutor, you have to make some tough calls.”
While it may repel some younger liberals, Ms. Harris’s history as San Francisco district attorney and California attorney general may be more asset than liability for more moderate voters, as it has been for Ms. Napolitano and so many women in politics who began their ascent as prosecutors.
That law enforcement pedigree, which Ms. Harris also shares with Mr. Biden’s late son Beau, is only part of the reason he turned to her, though.
He also chose her to help inject excitement into his campaign, which is leading in the polls but mostly because he’s the genial alternative to the most divisive president in modern history who is presiding over a pandemic and economic collapse.
Having started his career in a capital consumed with Watergate and controlled by white men, Mr. Biden also turned to Ms. Harris to bring a fresh perspective to the West Wing should they win — a similar calculation, but with the roles reversed between ticketmates, that propelled him to the vice presidency 12 years ago.
Mr. Biden spurned those progressives who wanted their consensus-oriented standard-bearer to elevate a liberal like Senator Elizabeth Warren, instead picking a prominent leader from the demographic that resurrected his campaign in the Democratic primary. By doing what Hillary Clinton did not do four years ago and choosing a Black running mate, he may give the party’s most loyal voters a reason, beyond animus toward Mr. Trump, to work for and elect the ticket.
Ms. Harris comes to the ticket having started her career in the crucible of San Francisco politics, won statewide office in America’s largest state and sought the presidency herself. She has a relationship with many party donors, lawmakers and activists. She has been scrutinized far more than some of the runners-up, who have either never been elected outside a House district or had never been on a ballot at all, as was the case with Susan E. Rice, the former national security adviser.
This is not to say that Mr. Biden simply made a politically safe choice.
Mr. Biden is now taking direct aim at Mr. Trump’s brand of racial grievance politics by making his political partner the daughter of Jamaican and Indian immigrants. In doing so, he passed over candidates like Gov. Gretchen Whitmer of Michigan who might have been more appealing to some white moderates and even Republicans in traditional battlegrounds like Wisconsin, Michigan and Pennsylvania.
Ms. Harris is also, like Mr. Biden, a candidate some Democrats may be glad is running in a coronavirus campaign free of rallies and short on spontaneity: While she can be extraordinarily effective when she’s well-prepared, Ms. Harris is less formidable and at times gaffe-prone when she’s off script.
Most consequentially of all, though, is what Mr. Biden’s decision may mean to the future of his party. Even though some of his own advisers expressed unease about any running mate who might quickly begin eyeing a future presidential bid, even in 2024 if he does not run again, Mr. Biden decided to give Ms. Harris a head start on becoming the country’s first female president.
No other aspiring president in the Democratic Party will enjoy the sort of platform of Ms. Harris, should she become vice president. Were Mr. Biden to win, she would be the only figure under 70 among the party’s leaders in the House, the Senate and the White House.
“It shows that Biden didn’t buy into this criticism of Harris being too ambitious,” said Ms. Napolitano, alluding to caricatures that infuriated many women but which made some of Mr. Biden’s supporters, and even staff members, leery of her.
In some respects, the Biden-Harris pairing represents the fulfillment of what many party activists hoped and expected would be their 2020 ticket, which they continued to whisper even in the tense days after the first Democratic debate last year when she sharply criticized him over his 1970s-era opposition to school busing.
Across the spectrum of the Democratic Party — former elected officials, grass-roots activists, swing-state moderates, and even much of the progressive wing — the reaction was largely a sigh of relief.
Many were energized about the selection of Ms. Harris, and at minimum, they felt she fulfilled many of the requirements their slice of the electorate preferred. More controversial picks were avoided. The overarching rule of “do no harm” was satisfied.
And for Black women in politics, Ms. Harris’s elevation was especially sweet — even if they acknowledged the somewhat conventional nature of her selection.
“Oftentimes do-no-harm choices are not exciting — this is an exciting one,” said Leah Daughtry, a decades-long veteran of Democratic campaigns, sharing that women were calling her in tears. “She is the stand-in for Black women. We are on the ticket.”
But by choosing Ms. Harris, Mr. Biden also stamped out the final hope of progressives who held out hope that recent victories in New York City, St. Louis and Chicago would force Mr. Biden to choose someone with left-wing bona fides.
Throughout their careers, both Mr. Biden and Ms. Harris have been pushed by the left, particularly on criminal justice, health care and the economy. Their responses have mirrored each other also: casting themselves as uniters at the center of the party. Their challenge now will be to unite a Democratic coalition that can bring in some of the voters Mr. Trump has put off, while motivating young people and progressives who may not see this ticket as representing their ambitions.
The length of Mr. Biden’s selection process had given a range of groups the opportunity to publicly lobby for their interests since March. None were louder than Black Democrats who angled for the selection to be a Black woman, a chorus that particularly intensified after the start of protests over racial inequality.
At times, it seemed Mr. Biden was being pulled in opposing directions: a governing pick ready to lead at any moment and one whose life experiences spoke to the country being torn apart by race and racism. In Ms. Harris, Mr. Biden and Democrats believe they have both.
Derrick Johnson, the president of the N.A.A.C.P., said Mr. Biden’s selection proved that he is prioritizing the Black electorate in the general election, and rewarding them for supporting him in the primary.
“It will energize Black voters because they can now see themselves in the ticket,” Mr. Johnson said. “By supporting Biden in the primary, the question was now how will they be reflected in his administration. And what V.P. Biden is saying is we’ll have a voice at the highest levels.”
The Rev. Al Sharpton, the civil rights leader and television show host, called Ms. Harris a “great selection.”
Mr. Sharpton, who said he talked to Mr. Biden “three or four times” during the vice-presidential selection process, said he believed that the national conversation about racial inequality pushed Mr. Biden to select a Black woman. He credited public pressure campaigns with creating an environment in which a non-Black woman would be seen as a slight.
“You had intergenerational and cross-the-board press on him,” Mr. Sharpton said, bringing up Representative James E. Clyburn, the highest-ranking Black Democrat in Congress. “If you have everyone from Clyburn and the Black caucus, to Sharpton and civil rights guys, and even the cultural figures and Black women, it clearly had an impact.”
But the reaction was strongest among Democratic women, who have known for months that Mr. Biden would select a woman as a running mate — but were nonetheless excited about the announcement. In Ms. Harris, the party has someone who made outreach to women a key aspect of her presidential run.
Nse Ufot, chief executive of the New Georgia Project, the organization seeking to flip the Southern state by registering new voters, said that “we all know that Black women have been the backbone of the Democratic Party and our leadership has gone uncredited for far too long.”
She invoked the name and words of Shirley Chisholm, the New York congresswoman who was the first Black woman to mount a national campaign for president. When Ms. Harris announced her presidential run in 2019, she chose the same week of Ms. Chisholm’s announcement as a homage, basing her color scheme and logo after her political hero, whose famous mantra was “unbought and unbossed.”
Nearly 50 years after Ms. Chisholm’s run, Ms. Harris carries Black women a step closer to the Oval Office — and reflects the evolution of Black Americans from political outsiders pounding on democracy’s doors to consummate insiders ushered into the clubhouse.
“Shirley Chisholm is smiling today,” Ms. Ufot said. “This is only the beginning, as there are many more of us bringing folding chairs to the table of democracy.”