Joe Biden has denied allegations that he sexually assaulted a former aide in 1993.
In his first public remarks about Tara Reade’s claims, the former vice president said: “They aren’t true. This never happened.”
The presidential candidate added that he is asking the National Archives to determine whether there is any record of Ms Reade filing a complaint.
Ms Reade, who used to work in the Senate, has accused Mr Biden of pinning her against a wall, reaching under her skirt and assaulting her in the basement of an office.
Pressure on the 77-year-old mounted this week after Ms Reade’s brother and a former neighbour said she had previously told them about part of her allegation.
The Democrats’ likely candidate to take on Donald Trump in November’s election had not previously publicly spoken about the allegation, but his campaign put out a statement last month denying it.
On Friday, he said: “While the details of these allegations of sexual harassment and sexual assault are complicated, two things are not complicated.
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“One is that women deserve to be treated with dignity and respect, and when they step forward they should be heard, not silenced.
“The second is that their stories should be subject to appropriate inquiry and scrutiny.
“Responsible news organisations should examine and evaluate the full and growing record of inconsistencies in her story, which has changed repeatedly in both small and big ways.
“But this much bears emphasising.
“She has said she raised some of these issues with her supervisor and senior staffers from my office at the time.
“They – both men and a woman – have said, unequivocally, that she never came to them and complained or raised issues.
“News organisations that have talked with literally dozens of former staffers have not found one – not one – who corroborated her allegations in any way. Indeed, many of them spoke to the culture of an office that would not have tolerated harassment in any way – as indeed I would not have.”
Mr Biden added that there is a part of Ms Reade’s story that can be verified, and that is her claim she filed a complaint against him in 1993, which he says does not appear in the papers he donated from his time in the Senate – as is the practice of senators – to the University of Delaware.
He said the only other place the complaint could be is in the National Archives so he has requested for her complaint, if it is there, to be made available to the press.
“If there was ever any such complaint, the record will be there,” Mr Biden said.
He added that he has spent his career “learning from women the ways in which we as individuals and as policy makers need to step up to make their hard jobs easier”.
He said he has fought for women’s health issues and basic women’s rights throughout his career and will continue to do so.
House of Representatives Speaker Nancy Pelosi said on Thursday that she still backed Mr Biden.
“I have complete respect for the whole #MeToo movement,” the fellow Democrat said.
“There is also due process and the fact that Joe Biden is Joe Biden. He is the personification of hope and optimism and authenticity for our country – a person of great values.”
She said those running Mr Biden’s Senate office at the time had no recollection of any complaint and that he had a long history of backing policies to protect women.
Other Democrats have been forthright in saying the claims are harming Mr Biden and that he should publicly address them.
“The campaign has issued statements, but he hasn’t issued any statements in his own voice,” said former Democratic National Committee chairwoman Donna Brazile.
“It’s not helping, it’s just damaging – not only to the person who has come forward, but it’s also damaging the candidate.”
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Claire Sandberg, who ran Bernie Sanders’ campaign, said the president would likely use the sexual assault claims against him.
“I think we have to apply a consistent standard for how we treat allegations of sexual assault, and also be clear-eyed about how Donald Trump will use these allegations in the general election campaign,” she said.
Mr Biden is the presumptive Democrat nominee for the first US election of the post-#MeToo era, scheduled for 3 November.
His likely opponent, Donald Trump, has also been accused of sexual assault by multiple women – claims he also denies.
The president told reporters on Thursday that Mr Biden should speak out.
“I don’t know anything about it, I don’t know exactly. I think he should respond,” said Mr Trump.
“So it could be false accusations. I know all about false accusations. I’ve been falsely charged numerous times.”
Mr Biden was also accused last year by another woman, Lucy Flores, of putting “a big slow kiss on the back of my head” during a campaign rally in 2014.
He responded at the time by saying he was a tactile person who had “offered countless handshakes, hugs, expressions of affection, support and comfort”.
He said he believed he had never acted inappropriately.