WASHINGTON — In the week since President Joe Biden’s dismal debate performance, Vice President Kamala Harris has emerged, publicly and privately, as one of his fiercest defenders — and as the person with the most intense support to succeed him on the ticket if he were to step down.

NBC News spoke with seven sources who have stressed that while Harris is focused on building up confidence in Biden, her loyal allies are making it clear that should the chance emerge for her to step into the lead role, she would have broad support across the party. Those allies, who include a number of Black Democrats, have vocally said any attempt to push her aside this year would be met with forceful, vocal pushback.

“I think she’s done very well on her feet,” said the Rev. Al Sharpton, who added that while he continues to support Biden as the party’s nominee, Harris should not be passed over should Biden drop out. “She’s always been good. I think she’s just better. And I think that she’s better than any of the names that have been floated out there.”

Sharpton, a civil rights activist and an MSNBC host, added there is “no doubt” in his mind that the motivation of anyone trying to cast aside Harris, the first woman, Black person and person of South Asian descent to serve as vice president, is “racist and misogynist.”

“If anyone tried it, they better know I’m on the tracks to block the train from going ahead,” Sharpton said of any effort to make someone other than Harris the top of the ticket. “When people voted for Biden to be the nominee, they were voting for the Biden-Harris ticket. How are you going to now come and separate that ticket and throw it open? There is no legitimate excuse. The calculation is ‘We can do this because she’s a woman and because she’s Black.’ Well, Blacks and women should not tolerate that calculation.”

Minutes after the debate, Harris was already on television delivering a forceful defense of Biden. Three sources familiar with the series of interviews said Harris received no official talking points from the campaign and had very little time to prepare.

Her snap reaction gave Democrats a blueprint for defending Biden that has been repeated over and over again since she uttered these words on CNN: “I’m not going to spend all night with you talking about the last 90 minutes when I’ve been watching the last 3½ years of performance.”

Democrats have also followed her lead after she pointedly attacked former President Donald Trump for pushing “lies” and creating “damage across the country” and made it clear she was laser-focused on beating Trump in November. 

The impact of Harris’ ability to quickly push back against questions about Biden’s energy and capability for a second term has helped quiet some of the criticism that has dogged her for years, including questions about her effectiveness in the administration and her ability to win the presidency. The Biden campaign has circulated her interviews as talking points to defend the president, and some Democrats have quietly pointed to her performance as evidence that she should not be cast aside as the party’s candidate if Biden got out of the race. 

Meanwhile, Harris, herself, has been receiving phone calls from, and making phone calls to, dozens of party leaders, civil rights activists and donors to reassure them about the way forward with Biden as the nominee and to help unify the party, according to four sources who spoke directly with Harris in the past week. During those calls, Harris has reiterated that she remains loyal to Biden and that Biden has weathered tough storms in the past, including when his path in the 2020 primaries was uncertain.

A person familiar with Harris’ thinking said the message has been: “We are ready for this fight. Let’s stay positive. Head down. And let’s execute, because we have a lot of work to do.”

On Wednesday, Biden and Harris joined an all-staff call with their campaign team and delivered similar messages.

“We will not back down,” Harris said. “We will follow our president’s lead. We will fight, and we will win. … Joe Biden has devoted his life to fighting for the people of our country. In this moment, I know all of us are ready to fight for him.” 

Leah D. Daughtry, a Democratic political strategist with close ties to Harris’ office, echoed that sentiment and said Democrats need to focus on beating Trump.

“President Biden had a bad night,” Daughtry said. “I think to ignore the body of his work over these last 3½ years and what he has actually delivered in the course of his presidency is really quite unforgiving and quite stunning, in my opinion.”

Inside Harris’ office, she and her senior leadership have also consistently made it clear that staffers should remain focused on supporting Biden as the top of the ticket and on not engaging in talk of replacing him, said two sources granted anonymity to speak freely about the conversations.

Donna Brazile, a veteran Democratic political strategist and former chair of the Democratic National Committee, said talk of replacing Biden on the ticket is “an attack on the democratic process” and “utter nonsense.”

“How can we say we are the party to preserve and strengthen democracy and then overturn the will of the American people?” Brazile said. “That’s why none of us who are delegates are even having this conversation.”

Two sources also said Harris was not originally part of the White House’s July 4th celebration with Biden but was added to drive home their “unity” message as external pressure for Biden to drop out grows.

Still, even with Harris presenting a united front, many — including top Democratic donors and Democratic lawmakers — have questioned whether Harris should be the Democratic presidential nominee if Biden were to step down. Govs. Gavin Newsom of California, Josh Shapiro of Pennsylvania, J.B. Pritzker of Illinois and Gretchen Whitmer of Michigan have all been mentioned as potentially stronger choices to replace Biden.

And some congressional Democrats have whispered that Harris at the top of the ticket is an even scarier prospect than running with a diminished Biden, because many polls in recent years have shown her to be less popular than he is.

A Democratic congressional aide said numerous Democrats in tough races worry about the “chaos” that would ensue if Harris were the nominee. There are “definitely plenty of people who are pushed towards Biden because they are concerned about the alternatives faring less well, starting with her,” the aide said.

A Democratic strategist working on House races said the party’s candidates have been significantly outperforming Biden for months and have generally preferred to run with him rather than Harris atop the ticket. But after the debate, there was some shift.

“I’ve never heard so many people saying, ‘F— it, Kamala would be better,’” the strategist said. 

The questions about Harris’ ability to run at the top of the ticket have been met with deep frustration by a number of people inside the party, including many Black Democrats. 

Harris’ allies point out that she has successfully run for statewide office both as the attorney general of California and as a senator from the state. They also say she had distinguished herself in the last two years as the administration’s most prominent voice on abortion rights, a key issue for voters, and on topics like the economy, on which she has pushed hard to turn out Black, Latino and other voters of color.

Brazile, who remained adamant that the party is not planning to replace Biden, said that if Biden decided to step down, she and other Black women in the party would not allow Harris to be passed over. 

“If somebody wants to go past or look past the vice president of the United States and find someone else, if this was a legitimate scenario or conversation, they would still have to come past some of us,” Brazile said. “Black women are still the backbone of this party. We have been the backbone. And we will continue to help lead the Democratic Party. I’m not saying that we’re playing a race card or a gender card. We’re playing a leadership card. And Vice President Harris has been part of the leadership in this Democratic Party.” 

Meanwhile, Rep. James Clyburn, D-S.C., a Biden-Harris campaign co-chair who was instrumental in helping Biden win the nomination by endorsing him in the South Carolina primary in 2020, told MSNBC that he would “support” Harris if Biden “were to step aside.”

“This party should not in any way do anything to work around Miss Harris,” Clyburn said. “We should do everything we can to bolster her whether it’s in second place or at the top of the ticket.”

There is also the issue of money and who could use the Biden campaign account, which had $91.2 million in it as of May 31. On Sunday, during a tense call between campaign aides and donors, Julie Chavez Rodriguez, the Biden campaign manager, said that if Biden decided to step down, Harris would then control most of the money in the campaign account. And Harris donors have also started strategizing about what her candidacy would look like should Biden decide not to continue running.

A CNN poll released Tuesday also found that Harris would do better than Biden in a hypothetical match-up with Trump. According to the poll, 47% of registered voters would support Trump and 45% would support Harris, though the result is within the margin of error. Historically, though, Harris’ approval ratings have often lagged behind Biden’s approval, which has also been low.

Still, a number of people around Harris say she remains focused on reassuring elected officials and others that the debate has not meaningfully affected the race — on conveying that the president she works with every day remains in command of his duties, on rallying the pockets of the Biden-Harris coalition that need shoring up, including major-party donors and voters, and on prosecuting the case against electing Trump.

Her message, they said, remains much like what Harris said the day after the debate at a Los Angeles campaign event.

“Four things remain true before that debate and after that debate: The stakes are higher than they’ve ever been,” Harris said to applause. “This person [Trump] is a threat to our democracy. We have all of the right issues on our side in terms of what we are fighting for. And you know the fourth thing that remains true before the debate and after debate? Trump is still a liar.”