US Vice President Kamala Harris, building Democratic backing for her sudden presidential run, has rallied supporters with a debut campaign speech vowing to go after Republican nominee Donald Trump like the courtroom prosecutor she once was.
"I took on perpetrators of all kinds. Predators who abused women, fraudsters who ripped off consumers, cheaters who broke the rules for their own gain," Harris told campaign workers on Monday, 28 hours after President Joe Biden, 81, abandoned the 2024 White House race and endorsed her.
"So hear me when I say I know Donald Trump's type. In this campaign, I will proudly put my record against his," said Harris, who was attorney-general of California and a US senator before serving as Biden's vice president.
Trump is due to be sentenced in September after having been found guilty of falsifying business records to hide hush money payments to a porn star. He also faces criminal charges related to his efforts to overturn Biden's 2020 victory. He falsely claims he lost in 2020 because of election fraud.
Biden, who pulled out of the race on Sunday amid questions about his age and health, called into Harris' campaign event. Recovering from COVID-19 at his home in Delaware, he sounded hoarse but appreciative of his vice president.
Harris, 59, outlined a series of policies she promised to pursue including signing laws to protect abortion rights and ban assault rifles and said she would make rebuilding the middle class the focus of her presidency.
Within minutes of receiving Biden's backing on Sunday, Harris began consolidating Democratic support for her presidential bid, securing commitments from hundreds of convention delegates, announcing a massive fundraising haul and earning endorsements from top party figures.
The Harris campaign aims to secure commitments from a majority of the nearly 4000 Democratic delegates to next month's Democratic Party convention by Wednesday evening, sources told Reuters, effectively wrapping up the nomination.
Campaign officials and allies have made hundreds of calls urging delegates to nominate Harris for president in the November 5 election.
Harris' campaign said it raised $US81 million ($A122 million) in the 24 hours following Biden's exit, the most for a single day in the 2024 campaign for either party.
Biden's departure was the latest shock to a White House race that included his disastrous June 27 debate performance against former President Trump and the July 13 near-assassination of Trump by a gunman during a campaign stop.
Harris lauded Biden for his service to the country. At a White House event to honour college athletes earlier on Monday, she said: "Joe Biden's legacy over the last three years is unmatched in modern history."
Harris will travel on Tuesday to Milwaukee, the largest city in the battleground state of Wisconsin, which last week hosted a Republican National Convention that offered a stark display of Trump's dominance over his party.
Harris, who is Black and Asian American, would fashion an entirely new dynamic with Trump, 78, offering a vivid generational and cultural contrast.
The Trump campaign has been preparing for her possible rise for weeks, sources told Reuters. It sent out a detailed critique of her record on immigration and other issues on Monday, accusing her of being more liberal than Biden.
Trump, whose lies that his 2020 loss to Biden was the result of fraud inspired the January 6, 2021, assault on the US Capitol, on Monday questioned Democrats' right to change candidates.
"They stole the race from Biden after he won it in the primaries," Trump said on his Truth Social platform.
Most public opinion polls conducted before Biden dropped out did not find that Harris performed better statistically against Trump than Biden had.
