“I recognize my responsibility to be a voice, an advocate, and a leader for the change in culture that has begun but is nowhere near finished,” Mr. Biden wrote in a Medium post. “So I want to address allegations by a former staffer that I engaged in misconduct 27 years ago. They aren’t true. This never happened.”
He was expected to be interviewed about the subject on MSNBC’s “Morning Joe” later Friday morning.
At issue is an allegation from a former aide in his Senate office, Tara Reade, who has said that Mr. Biden assaulted her in 1993, when he was a senator from Delaware. His campaign has said her account is false, but Mr. Biden, who has participated in virtual fund-raisers and local television interviews in recent days, had not raised the matter himself or faced public questioning on the subject.
There have been growing calls for Mr. Biden to release his Senate papers, held at the University of Delaware. In the Medium post, Mr. Biden said that those papers “do not contain personnel files.” Instead, he called on the National Archives to release any existing complaint.
“There is only one place a complaint of this kind could be — the National Archives,” he wrote. “The National Archives is where the records are kept at what was then called the Office of Fair Employment Practices. I am requesting that the Secretary of the Senate ask the Archives to identify any record of the complaint she alleges she filed and make available to the press any such document. If there was ever any such complaint, the record will be there.”
While Mr. Biden has until Friday remained quiet on the subject, a number of prominent Democrats have been pressed on the matter and have sided with Mr. Biden even as Republicans and some activists on the left have been sharply critical.
“I want to remove all doubt in anyone’s mind: I have a great comfort level with the situation as I see it, with all due respect in the world for any woman who comes forward, with all the highest regard for Joe Biden,” Speaker Nancy Pelosi told reporters on Thursday.
“There is a lot of excitement around the idea that women will be heard and be listened to,” she said, expressing “complete respect” for the #MeToo movement. “There is also due process, and the fact that Joe Biden is Joe Biden.”
Some of Mr. Biden’s potential running mates, including Senators Amy Klobuchar of Minnesota and Kamala Harris of California, as well as Stacey Abrams, the former Georgia House minority leader, have also voiced support for Mr. Biden, noting his work, for instance, on the Violence Against Women Act.
Some Republicans have sought to paint Democrats as hypocrites, suggesting that they are holding Ms. Reade’s allegation to a different standard compared with the one used for accusations of sexual assault against Brett M. Kavanaugh during his Supreme Court confirmation hearings in 2018.
“I think he should respond,” President Trump said of Mr. Biden on Thursday, as his campaign signaled this week it intended to make the allegation a campaign issue. “It could be false accusations.”
At a fund-raiser on Wednesday, Mr. Biden was asked about combating sexual assault in the military.
“Ignoring sexual assaults in the ranks goes against everything the military itself stands for,” he said. “It corrodes unit trust. It endangers everyone in the unit. It literally is a life-and-death issue if you can’t trust the person you’re standing beside, if they have your back.”
He detailed his own history of leading efforts to combat sexual violence. But he did not address the allegation he is facing now.