As President Biden battles Democratic doubts about his ability to beat Donald Trump after a damaging debate and Trump’s string of legal and political victories, Harris — now the vice president — is again her party’s heir apparent.

If she becomes the Democrats’ nominee for president, the first Black, Asian American and female vice president will have to answer questions about her last campaign for the top job, an effort that collapsed before a single ballot was cast. Critics say Harris squandered her considerable potential by mismanaging her 2020 campaign, struggling to project authenticity and stumbling as a candidate.

“She was always the dream for us, of the next phase beyond Obama, but she didn’t live up to it because she ran a terrible campaign,” said one Democratic strategist who spoke on the condition of anonymity, referring to 2019.

Five years later, Harris’s allies argue, she has improved as a politician and manager. Her boosters say that her 3½ years as Biden’s No. 2 would help her quickly adjust to being thrust atop the ticket, if she finds herself there. They say Democrats should no longer be worried about Harris’s initial stumbles because she has improved how she communicates and shifted how she is perceived.

Now, her defenders say, she is a bright spot during a dark moment for Democrats.

“You see her becoming more comfortable with being a vice president,” said Bakari Sellers, a former South Carolina state representative and longtime Harris supporter who has also defended Biden as the nominee. “And she now has a team of people around her that have strengthened her, and the stories that are coming out of D.C. are changing. The narrative has changed.”

This story is based on interviews with nearly a dozen of Harris’s veteran supporters and aides, who argue that the sour taste left from her presidential campaign has faded, evidenced by a growing number of Democrats who see her as a viable Plan B if Biden exits. Some of these supporters spoke on the condition of anonymity to talk candidly at a critical moment.

Harris, through a spokesperson, declined to be interviewed. She has championed Biden since the night of the debate, declaring repeatedly that he is the nominee and she is his running mate and encouraging others to “fight for him.”

If Biden steps aside, an easy coronation for Harris is far from guaranteed. Some Democratic power brokers are mulling an “open convention,” in which the presidential nominee is chosen on the fly. If she’s the nominee after the convention, Harris would face an impassioned GOP that has already intensified its attacks against her.

But even with those hurdles, she would be closer to winning the presidency than she ever was in 2019.

Harris’s stumbles began shortly after she announced she was seeking the White House.

In April 2019, she expressed regret over a policy she championed that prosecutors used to bring charges against the parents of truant children. Prosecutors took parents across the state to court, and some were jailed, though never directly by Harris. The moment highlighted concerns by some Democrats that Harris was a product of an inequitable criminal justice system.

By June, as primary opponents like Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.) had staked out their positions on a broad range of economic and social policies, Harris struggled to articulate what, exactly, her administration would look like, instead hewing to long-held (and mostly safe) mainstream Democratic positions.

During a debate that month, Harris was one of two who raised her hand when moderators asked which candidates would abolish private health insurance. A day later, Harris changed that answer, saying she had misheard the question.

In July, her campaign put 35 additional staffers in Iowa and 25 in New Hampshire, following months of criticism that she had not made the two early-voting states a priority. Two months later, she adopted an Iowa-first strategy, hiring 60 more staffers in the state as she dropped behind other candidates in polls.

By November, dwindling funds had forced her to retreat at a point when her campaign advisers expected her to be surging. By the next month, her presidential bid was over.

Still, supporters say it showcased her potential as a campaigner and her ability to energize a younger, more diverse party powered by women. Biden selected her as his running mate in August 2020, making good on a promise to put a woman on his ticket. In doing so, he anointed Harris as the future of the party.

Biden referred to his presidency as the “Biden-Harris” administration from the outset, instead of using solely his name, as previous presidents had done — a vote of confidence in his decades-younger vice president.

Still, in her first year in the White House, Harris struggled at times to communicate, including in a Lester Holt interview from Guatemala, where she was dispatched to try to address the root causes of migration. During the interview, she ended up committing to go to America’s southern border, giving oxygen to Republican efforts to tie her to migrant crossings.

Harris’s supporters say she is under a more intense microscope than most politicians and certainly most vice presidents, who have often been footnotes in presidential history. Harris entered the history books the moment she was inaugurated as the first woman and the first person of Black and Asian descent to win a nationally elected office.

“People expected her to make history every time she walked into a room,” one former staffer said, adding that many of the attacks appeared to be rooted in racism and misogyny. “It was an impossible standard.”

Major news organizations carved out lines of coverage centered on the vice president. The Los Angeles Times, her home-state newspaper, tracked her vice-presidential approval ratings. But former staffers say she eventually adjusted to the sometimes searing scrutiny.

“Part of (it) is getting comfortable with all the cameras on you all the time,” said one former aide, who spoke on the condition of anonymity to give a candid analysis. “Even people at that level of the stratosphere have to learn how to get comfortable with it — that everything they say is going to get scrutinized. That people will not be forgiving about the time of day that they’re doing an event. You say something, and suddenly it gets scrutinized at a very high level, in terms of the number of cameras, in terms of the reach.”

That scrutiny was perhaps most intense at the end of Harris’s first year as vice president, amid several high-profile staff departures, including her chief spokesperson, her communications director and her chief of staff. The resignations reignited questions about why Harris churns through top-level Democratic employees, an issue that has dogged her for almost all of her time in public service.

The drumbeat of unflattering anecdotes took a toll. Some Democrats found her tenure as vice president underwhelming, marked by the messaging struggles and, at one point, near invisibility. It left many uncertain whether she had the force, charisma and skill to win the White House on her own. And some cast about for alternatives to lead the party into the future.

Then the Supreme Court overturned Roe v. Wade, and Harris’s strategy — and reputation — shifted. She took dozens of trips to Democratic strongholds and battleground states, warning that the Supreme Court decision was an example of Republican overreach that would intensify if voters didn’t send them a message at the ballot box. And Biden’s team increasingly saw her as an important electoral asset, particularly in reaching younger voters and people of color, whose enthusiasm for the president appeared to be slipping.

“The highest court in our land — the court of Thurgood and RBG — right? — took a constitutional right that had been recognized from the people of America, from the women of America. And now, we must speak of Roe in the past tense,” she said during a February event in Savannah, in the battleground state of Georgia.

Other weaknesses that limited Harris in the 2020 primary have also been addressed, her supporters argue.

One attack Biden used against Harris and other Democrats in 2020 was his personal relationships with a wide swath of world leaders, often name-checking them in debates and campaign appearances. But since becoming vice president, Harris has been the keynote speaker at the Munich Security Conference three times, rallying the European continent as Russia invaded Ukraine. She has sought to fortify allies in South Korea, Tokyo and Southeast Asia and to improve conditions in Northern Triangle countries, from which a vast number of immigrants to the United States come.

She’s also shaken up her team. The vice president has a new chief of staff, Lorraine Voles, who was the director of communications for then-Vice President Al Gore and former senator Hillary Clinton. There have also been changes among staffers who help shape the vice president’s public image. And Anita Dunn, one of Biden’s closest political strategists, has focused more intensively on the vice president’s schedule and public events.

But while supporters say Harris’s handling of the job has improved, she is also benefiting from a changed political landscape — one that is more favorable to her.

In 2019, Harris was one of two dozen Democrats who vied for the presidential nomination — jockeying for top talent on their campaigns, cash from donors and, most importantly, voters’ attention. Harris’s story and her role as one of few Black women who have the reached the Senate were powerful symbols. But she was largely unknown nationally. Her campaign staff was filled with California politicos trying to make inroads in communities far removed culturally and geographically from the Golden State.

If Harris suddenly becomes the Democrats’ 2024 nominee, she would have the support of the entire Democratic campaign establishment, which is desperate to beat Trump a second time. She has name recognition on par with any national politician, and the Biden-Harris campaign has already raised nearly a quarter-billion dollars that would flow to her.

“The party and the structure of the party will all do the same to get behind her,” the Democratic strategist said. “So it’s not going to be about her, really. There’s no time for her to decide what the campaign looks like. That’s not going to happen. What is going to happen in this campaign for five months — it’s already been laid out.”

Chelsea Janes, Isaac Arnsdorf and Paul Kane contributed to this report.