Brett Kavanaugh has dismissed two new claims of sexual assault, including watching an alleged gang rape, as "from the Twilight Zone".
Donald Trump's US Supreme Court nominee now has four women alleging criminal behaviour against him.
One of the new accusers, Julie Swetnick, says in the early 1980s Mr Kavanaugh and friends would regularly get girls drunk or drugged so they wouldn't "say no".
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"I have a firm recollection of seeing boys lined up outside rooms at many of these parties waiting for their 'turn' with a girl inside the room," she wrote in an affidavit supplied to the Senate Judiciary Committee, which is investigating the claims against Mr Kavanaugh before he's sworn in for life.
She says at one party in 1982, she was the girl.
"During the incident I was incapacitated without my consent and unable to fight off the boys raping me," she wrote. "I believe I was drugged using Quaaludes or something similar placed in what I was drinking."
Though stopping short of saying Mr Kavanaugh was one of the alleged rapists, Ms Swetnick says he was at the party.
"This is ridiculous and from the Twilight Zone," Mr Kavanaugh said in a statement. "I don't know who this is and this never happened."
Ms Swetnick is being represented by Michael Avenatti, the lawyer who's representing porn actress Stormy Daniels in her legal battle with the US President. He told MSNBC his client is an "honest and courageous" woman.
"If they try to come after my client or engage in some smear campaign, they better pack a lunch because we're going to respond twofold. We are going to respond double as it relates to force. So they better be very careful before they start spewing nonsense and trying to call my client a liar."
Mr Trump, who has been accused of sexually inappropriate behaviour and even admitted to grabbing women's privates, told a news conference the allegations were "all false" - but also said he was open to changing his mind.
"I'm going to see what's said. It's possible they will be convincing... I can't tell you if they're liars until I hear them."
He went on to call the claims a "big fat con" orchestrated by his political opponents, and said even George Washington, the country's first President, probably had "a couple of bad things in his past" Democrats would use to malign him.
The identity of the fourth accuser is not yet known. NBC News reported the accusation was delivered in a letter to a Senator's office, and doesn't have a name or a return address or contact info.
It alleges Mr Kavanaugh shoved a woman up against a wall "very aggressively and sexually" while he was drunk, NBC News said.
Mr Kavanaugh said that accusation too was from the Twilight Zone.
"We're dealing with an anonymous letter about an anonymous person and an anonymous friend... It's ridiculous."
A vote on Mr Kavanaugh's nomination to the US Supreme Court was originally scheduled for September 20, but was postponed so the Senate Judiciary Committee could conduct its investigation.