Vice-President Kamala Harris has secured the support of a majority of Democratic delegates to become the party's nominee for president.
A survey by the Associated Press on Monday evening said she had received the endorsement of more than the 1,976 delegates needed to win the nomination in the first round of voting.
That means Ms Harris is on course to be crowned the party's standard bearer and take on Republican Donald Trump in November's presidential election.
It becomes official when party delegates hold a roll call vote ahead of next month's Democratic National Convention (DNC) in Chicago.
Delegates are people who are selected to represent their electoral area. Their pledges of support are non-binding until the vote but unlikely to change.
No-one has publicly stepped forward to challenge Ms Harris since President Joe Biden left the race on Sunday.
He found himself under mounting pressure from senior members of his party following his stumbling debate performance against Trump.
If the total holds between now and when delegates cast their votes, scheduled to take place from 1-7 August, Ms Harris would formally clinch the party's nomination.
The survey by AP is an indication of the groundswell of support for Ms Harris after President Joe Biden dropped out of the race on Sunday.
Since Mr Biden's announcement, millions of dollars in donations have poured into her campaign and leading Democrats have lined up to support her bid as the Democratic nominee.
Speaking to staff at her campaign's headquarters in Wilmington, Delaware, on Monday evening, Ms Harris had Trump in her sights.
Referring to her early career as a prosecutor in California who took on predators and fraudsters, she added: "I know Donald Trump's type."
She said the Biden-Harris campaign had always been about two different versions of the future of the country - theirs and Trump's.
"One focuses on the future, the other focuses on the past," she said. "Donald Trump wants to take our country backwards... we believe in a brighter future that makes room for all Americans."
She also noted Mr Biden's accomplishments, saying her time serving as his vice-president was "one of the greatest honours of my life".
Before Ms Harris took to the stage, Mr Biden made his first comments since dropping out of the 2024 election via phone call while isolating after contracting Covid-19.
He thanked aides and told them to "embrace" Ms Harris because "she's the best".
"I know yesterday's news was surprising and hard for you to hear, but it was the right thing to do," Mr Biden told them.
He vowed to remain fully engaged in the campaign because democracy was at stake.
Meanwhile Trump's new running mate, Senator JD Vance, attacked both Ms Harris and Mr Biden while campaigning in Virginia.
“History will remember Joe Biden as not just a quitter, which he is, but as one of the worst presidents in the history of the United States of America,” he said.
“But my friends, Kamala Harris is a million times worse and everybody knows it. She signed up for every single one of Joe Biden’s failures, and she lied about his mental capacity to serve as president.”
