Kamala Harris stares down yet another path with little precedent

The 59-year-old Harris has been thrust into a political maelstrom with little modern precedent. The last time a president chose not to run for re-election was in 1968, when Lyndon B. Johnson opted out.

As Harris seeks to rally support from her party, she isn’t guaranteed the nomination and will have to earn the required delegates to take Biden’s place at the party’s convention in August.

But she has a leg up over the governors and lawmakers who may jump in to the contest or be recruited by donors to compete. Biden made clear Sunday, after he announced he would stand down, that she is his pick to be the nominee.

“My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it’s been the best decision I’ve made," Biden wrote on X. “Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year. Democrats—it’s time to come together and beat Trump. Let’s do this."

Harris would be able to use the money already raised by Biden’s campaign committee and would likely have backing from some key lawmakers, such as influential Rep. Jim Clyburn (D., S.C), who has praised Harris.

Many Democrats have said that Harris is popular enough in the party—particularly among women and Black voters—and that casting her aside could cause resentment and division. The daughter of Indian and Jamaican immigrants, Harris has campaigned extensively on college campuses, in cities and before women and minority voters.

Harris is also a strong voice on what may be the Democrats’ most powerful electoral issue, abortion. She has led the administration’s message on abortion since the 2022 Supreme Court ruling that eliminated the right to the procedure, delivering a personal and legal argument as a former prosecutor.

It is far from clear that Harris, as her party’s presidential nominee, would satisfy the many Americans who say they are looking for an alternative to Biden and Trump. Several surveys earlier this year and last year found her performing about the same as Biden when tested against Trump. Many surveys including a recent Wall Street Journal poll after the president’s disastrous late-June debate performance found voters view Harris just about as unfavorably as they view Biden.

Trump’s campaign has already featured Harris in a TV ad emphasizing the president’s age. “You know who’s waiting behind him, right?" the narrator asks in the ad, with a video of Harris on the screen.

Ahead of Biden’s re-election campaign, some Democrats privately expressed concerns about Harris’s place on the ticket, portraying her as a liability and arguing she didn’t have the same appeal as Biden. Many Democrats dismissed such attacks on the first Black woman to serve as vice president, calling them unfair and arguing that she is being held to a different standard than others, including Biden.

Harris has long made clear that if necessary, she is prepared to step up. The vice president said in an interview with the Journal earlier this year: “I am ready to serve. There’s no question about that." Everyone who sees her on the job, Harris said, “walks away fully aware of my capacity to lead."

In the weeks since Biden’s debate performance ignited concerns about his age and mental acuity, Harris has been a stalwart cheerleader for her boss. She has said in interviews and on the campaign trail that he remains up to the task of serving, declaring the election wouldn’t be decided by “one night in June." But as criticisms mounted from donors and elected officials, it became increasingly clear that Biden couldn’t hold on.

Since the debate, Republicans have accused Harris and other Democrats of covering up Biden’s decline. “They are all co-conspirators in the sinister plot to defraud the American public about the cognitive abilities of the man in the Oval Office," Trump said at a recent Florida rally.

The White House and top aides have said Biden remains a sharp and vigorous leader.

The highest-ranking woman ever in the line of presidential succession, Harris grew up in Berkeley, Calif., and was raised by a single mother who immigrated from India at the age of 19.

She became the first woman to serve as California’s attorney general and was elected to the U.S. Senate in 2016, where she drew attention for her pointed questioning of then-judge Brett Kavanaugh during his contentious confirmation hearing. But she faltered in her bid for the 2020 Democratic nomination for president, struggling to frame a campaign message and dropping out before the primaries started.

During Harris’s early days in the White House she struggled to address issues such as border security and drew scrutiny over staff departures and criticism for her political skills.

But she has drawn praise in recent months as she has taken on more responsibility. In addition to abortion messaging, she has also beefed up her national-security portfolio, joining Biden on calls with Israeli Prime Minister Benjamin Netanyahu and pushing administration officials to articulate more empathy for Palestinians and to focus on a plan for postwar Gaza.

Write to Catherine Lucey at catherine.lucey@wsj.com and Tarini Parti at tarini.parti@wsj.com