A fourth accusation of sexual misconduct against Supreme Court nominee Brett Kavanaugh emerged Wednesday evening with four alleged witnesses, just hours before he is set to testify after his first accuser tells her story to a key Senate panel.

NBC News first reported an anonymous letter sent to GOP Sen. Cory Gardner of Colorado, in which a woman claims her daughter witnessed a drunken Kavanaugh assaulting a friend  in a sexual manner after a night of heavy drinking in the Washington, D.C., in 1998.

“When they left the bar … they were all shocked when Brett Kavanaugh, shoved her friend up against the wall very aggressively and sexually,” the letter’s author claims. “There were at least four witnesses including my daughter.”

Earlier Wednesday, a third accuser came forward alleging Kavanaugh sexually assaulted her when he was still in high school. She also claimed she saw him line up for “gang rapes” at parties. President Donald Trump, who wants to get Kavanaugh confirmed as the nine-member high court’s fifth and decisive conservative justice, defended him throughout the day.

At one point, the president referred to Kavanaugh as a “gem.” Later, during a wild press conference wrapping up a UN conference in New York, Trump accused Democrats of running a “big, fat con job” to “destroy” Kavanaugh and his family.

Asked about a fourth accuser who reached out to a Democratic senator alleging sexual misconduct by Supreme Court nominee Brett Kavanaugh, White House principal deputy press secretary Raj Shah said: “This is a completely anonymous letter and he didn’t even socialize with someone from Boulder at the time.“

Shah and another White House spokeswoman pointed to Kavanaugh’s private testimony with the Senate Judiciary Committee in which he denied allegations that surfaced Wednesday evening

“No, and we’re dealing with an anonymous letter about an anonymous person and an anonymous friend. It’s ridiculous. Total twilight zone. And no, I’ve never done anything like that,” he said, according to transcript excerpts provided by the White House.

Kavanaugh was the asked several other questions about the alleged incident. He answered “no” each time.

Senate GOP leaders insist the Judiciary Committee could vote Friday on the nomination, with floor votes to follow early next week. But it is not clear moderate Republicans are yet prepared to vote in favor of putting the federal judge on the high court.

And Trump on Wednesday left open the door to withdrawing the nomination if Ford convinces him Kavanaugh is guilty of her charges.

Around 8:30 p.m., the Trump campaign sent a text message to supporters urging them to sign an online petition supporting Kavanaugh.

“Democrats have incited a witch hunt against an innocent man with an impeccable reputation,” according to the petition posted on the campaign’s website.

Watch: Trump on Believing Kavanaugh Allegations: ‘I Have to Watch Tomorrow’