Kamala Harris, the vice president of the United States, has praised her boss, President Joe Biden, a day after he dropped out of the presidential race and endorsed her as his successor.

“Joe Biden’s legacy of accomplishment over the last three years is unmatched in modern history,” Harris said on Monday in her first public appearance since the 81-year-old US leader abruptly announced his withdrawal from the November polls a day earlier.

“In one term, he has already surpassed the legacy of most presidents who have two terms in office,” Harris said at a White House event to honour college athletes, where she was filling in for Biden, who is recovering at his home in Rehoboth Beach, Delaware, after testing positive for COVID-19 last week.

In her statement, however, Harris, 59, did not specifically refer to her new status as the leading Democratic candidate to replace Biden as the party’s presidential nominee.

Meanwhile, virtually all of the prominent Democrats who had been seen as potential challengers to Harris have lined up behind her, including Nancy Pelosi, the former speaker of the House of Representatives and one of the longest-serving and best known Democrats.

Pelosi, who remains influential since stepping down as speaker in 2022, played a leading role in persuading Biden to end his campaign amid concerns over his mental acuity and ability to beat Republican Donald Trump or to serve another four years.

“With love and gratitude, I salute President Biden for always believing in the possibilities of America and giving people the opportunity to reach their fulfillment,” Pelosi, 84, said in a statement on Monday.

“We must unify and charge forward to resoundingly defeat Donald Trump and enthusiastically elect Kamala Harris as the next President of the United States.”

Biden and Harris have been working together since 2020. As the US president solidified his lead in that year’s election, he promised he would select a woman as his running mate. The selection of Harris was seen as an effort to appeal to Black voters and energise the party’s base.

On Sunday, while declaring he was abandoning his re-election campaign, Biden wrote on X that his endorsement of Harris has been “the best decision” he has made.

Campaign officials and allies have already made hundreds of calls on Harris’s behalf, urging delegates to next month’s Democratic Party convention to join in nominating her for president in the November 5 election against Trump.

The new party nominee will be chosen at the convention in Chicago next month when more than 4,000 party officials and activists will gather to vote.

Harris could, however, still face challengers seeking the Democratic nomination in the coming days.

Rebekah Caruthers, vice president of the Fair Elections Center, told Al Jazeera Harris has a solid record when it comes to winning elections.

“She has been on the ballot many times, with being a district attorney, California attorney general. She herself ran for president during the 2020 cycle,” Caruthers said.

“One thing that the Harris campaign has been putting out: Each time Kamala Harris is on the ballot, she wins her election.”

But some Democrats were concerned about a Harris candidacy, in part because of the weight of a long history of racial and gender discrimination in the US, which has not elected a woman president in its nearly 250-year history.

“We should all prepare for the onslaught of attacks that would face any historic candidate,” Representative Alexandria Ocasio-Cortez told reporters. “Misogyny in our politics is far from over. Racism in our politics – especially confronting Donald Trump as a an opponent – is far, far from over.”