Sen. Kamala D. Harris clapped along with protesters near the White House chanting “Hands up! Don’t shoot!” A few days later, she passionately defended an anti-lynching bill on the Senate floor. And this week, she warned that America has “still not fully embraced, acknowledged or addressed its history of racism.”

As Harris (D-Calif.) seizes an outspoken role supporting the protests gripping the nation, top Democrats — including allies of Joe Biden in touch with his presidential campaign — increasingly see her as the strong favorite to become his running mate.

“I think she’d be great,” said Rep. Marcia L. Fudge (D-Ohio). “I think that she absolutely checks all the boxes.” Fudge, who wants Biden to pick a black woman, added, “This is the opportunity to show the diversity that we were all so excited about when this campaign started.”

But while Harris is championed by Democratic officeholders and leaders, who see her as appealing to suburban and centrist voters, many of the activists who have helped energize the street protests warn that party figures are missing the mood of the moment. As a traditional politician and former prosecutor, they say, Harris would fail to capture the passions that are powering the protests, and her selection could dampen the excitement that is crucial to the Democrats in November.

“I think that he needs to figure out somebody that’s not just there because they’re a black woman, because they check a box,” said Tay Anderson, 21, a Denver school board member and a leading voice in that city’s protests. “Nominating Kamala Harris in the wake of what’s going on is not the best solution. Nominating someone who’s put black people in jail doesn’t make sense at this moment. You have to have someone who’s not just a box- checker.”

Within Biden’s orbit of allies and confidants, there is a sentiment that picking Harris increasingly makes sense, according to three people in touch with the campaign who spoke on the condition of anonymity to be candid on a sensitive topic.

Biden holds a clear lead in the polls over President Trump, and some Biden allies have concluded that whomever he picks should invite little political risk and reduce the potential for drama. Harris is largely in ideological alignment with Biden and understands the workings of the federal government, they say.

Biden’s running mate search has been unlike any other. He has declared he will pick a woman, and the protests have added pressure for her to be African American. The number of black women in national political roles is relatively small — Harris is the only one who is either a senator or governor, let alone a recent presidential candidate.

Beyond Harris, Atlanta Mayor Keisha Lance Bottoms (D), who has won plaudits for her response to George Floyd’s death and the resulting protests, is mentioned as a potential running mate by some Democrats. Rep. Val Demings (D-Fla.), a former police chief, has also forged a bigger presence. Former U.N. ambassador Susan E. Rice and ex-Georgia gubernatorial nominee Stacey Abrams have shown strong interest in the job.

Harris has been cautious in discussing the role she envisions for herself. “I’m honored to be part of the conversation, and the vice president is going to make a decision that I’m sure will increase his ability to win,” she said in an interview. “And I want him to win, just about as much as I want anything else in life right now.”

But her growing prospects are evident in other ways. Harris and Biden appeared at a virtual fundraiser Tuesday that illustrated their personal dynamic. “She’s been a fighter and a principled leader — and I know, because I’ve seen her up close,” Biden said.

He mentioned Harris’s friendship with his son Beau Biden, who died of brain cancer in 2015, and he recalled running into Harris when he taught at the University of Pennsylvania. “You said, ‘I love you and I loved Beau,’ ” Biden said. “I won’t forget that.”

The running mate search, and its increasing focus on black women, represents a reversal of the Democratic presidential primary, which initially featured the most diverse field in history, including Harris, the daughter of Jamaican and Indian immigrants, but was dominated by white candidates as the field narrowed. The last two candidates standing — Biden and Sen. Bernie Sanders (I-Vt.) — were white men in their 70s.

Still, Harris’s prospects are not without complication. Although her experience as a presidential candidate is considered an asset, her campaign was plagued by infighting and collapsed before a single vote was cast.

She launched a blistering attack against Biden on school busing and race during a presidential debate last summer, which Biden’s wife Jill Biden later said landed “like a punch in the gut.”

And her record as a prosecutor, which some critics argue was overly harsh, is facing renewed scrutiny in the current environment, given protesters’ heavy focus on the criminal justice system. Harris herself argues that she was a progressive prosecutor, fighting racial injustice from within the system.

Beyond that, however, lurks a deeper question about the nature of the political moment. The demonstrations have showcased a resurgent black activism, often with support from white Americans that was absent in previous eras. That’s prompted a rethinking of the country’s fundamental approach to racial issues, raising questions about whether America’s leaders have long been too complacent in confronting racism.

Amid that turmoil, some question whether Harris would meet indifference or even a backlash from those urging a broad societal overhaul, and they warn about a potential lack of passion for the ticket. And other contenders and their allies are underscoring their abilities to excite the party.

“That’s one of the things we hear a lot about Joe Biden,” said Tharon Johnson, an adviser to Bottoms, the Atlanta mayor, who touted her credentials. “No one’s really willing to run over brick wall or crawl over broken glass” for him. Still, Biden “has proven he’s a fighter,” Johnson added, and “we just need someone to build upon the enthusiasm, to really cultivate the base.”

Harris, who appears acutely aware of these pitfalls, is mounting a vigorous effort to shore up her possible weaknesses. Her once sprawling and leak-prone political operation is leaner, and she is getting new credit from the activist wing of the party, which at times was openly hostile during the primaries.

Lenard Larry McKelvey, who goes by Charlamagne tha God as host of “The Breakfast Club,” a radio show popular with black audiences, said he now leans toward Harris as Biden’s running mate. “She’s tough, and she makes old white men nervous,” he said.

McKelvey supported Harris in the primary, but also said last year that she was “terrible” in one of the debates.

Biden, who has said he plans to name a running mate around Aug. 1, has kept the process tightly guarded.

In an interview with CBS News broadcast Tuesday, Biden said the protests of the past two weeks have not affected his thinking on a running mate, “except it’s put a greater focus and urgency on the need to get someone who is totally simpatico with where I am.”

Even with prominent African American women in the mix, Sen. Elizabeth Warren (D-Mass.) and Michigan Gov. Gretchen Whitmer (D), who are white, are seen by Democratic leaders as potential running mates. In contrast, the chances of Sen. Amy Klobuchar (D-Minn.), who is also white and was once viewed by Biden allies as a leading contender, have been diminished, some of them believe.

The killing of Floyd, a black man who lost his life after a white Minneapolis police officer knelt on his neck as he cried out that he couldn’t breathe, triggered a national outcry against police violence. That damaged Klobuchar, a former Hennepin County attorney, as critics contend she was too tough on black and brown people and not hard enough on police during her tenure.

Since departing the presidential race, Harris has become one of Biden’s most active surrogates, participating in live-stream events with his campaign and helping raise money. The event with Biden on Tuesday raised a hefty $3.5 million for a joint fundraising vehicle that includes Biden’s campaign.

Away from the campaign trail, Harris has kept busy on the issues at the forefront of the national conversation. On Monday, she appeared with congressional Democrats at a news conference promoting a sweeping new police reform bill. Harris has also unveiled legislation to fight racial disparities in the coronavirus pandemic.

When Sen. Rand Paul (R-Ky.) recently called for amending a bill that makes lynching a federal hate crime, citing concerns that it could allow enhanced penalties for lesser offenses, Harris took to the Senate floor to say, “The idea that we would not be taking the issue of lynching seriously is an insult.”

In recent years, many of Harris’s standout moments have come in the Senate, where she has developed a reputation for posing tough questions to Trump nominees at Judiciary Committee hearings. On the presidential campaign trail, however, she proved to be a shakier candidate who sometimes had to clarify her public comments.

This week, Harris won some Democratic praise for navigating an interview on ABC’s “The View.” When pressed on calls by some activists to “defund the police,” she pointedly asked questioner Meghan McCain how she was defining that term — putting McCain on the defensive before repeating her call for rethinking how public safety funds are distributed.

Personal relationships have long been important to Biden, and Harris has also made a point of reaching out in nonpolitical ways. Her friendship with Beau Biden dates back years to their time serving as state attorneys general, Harris in California and Beau in Delaware. Harris recently posted a smiling photo of the two of them on Twitter to honor his memory five years after his death.

“You couldn’t find a man with more principle and courage who cared deeply about his family and the nation he served,” Harris wrote, adding that she was thinking of Joe and Jill Biden and their family that day.

During Tuesday’s fundraiser, Harris said her husband, Doug Emhoff, had enjoyed spending time with Jill Biden, and they’ve stayed in touch beyond the primary. “There’s a special bond between the spouses,” she said.

Cleve R. Wootson Jr. contributed to this report.