Washington, D.C.: The woman who has accused President Donald Trump’s Supreme Court nominee of sexual assault all but ruled out appearing at an extraordinary Senate hearing scheduled for next week to hear her allegations, insisting on Tuesday that the FBI investigate first.

Speaking through lawyers, Christine Blasey Ford said she would cooperate with the Senate Judiciary Committee and left open the possibility of testifying later about her allegations against Judge Brett M. Kavanaugh. But echoing Senate Democrats, she said an investigation should be “the first step” before she is put “on national television to relive this traumatic and harrowing incident.”

Republicans signalled on Tuesday night that they would not negotiate an alternative date and would go ahead with the hearing without her or declare it unnecessary if she refuses to appear, then possibly move to a vote. They have repeatedly stressed that Monday would be Blasey’s opportunity to testify, either privately or publicly, and that they planned to move forward with the confirmation process afterward.

The apparent standoff was yet another turn in a high-stakes drama over the president’s second Supreme Court nominee that began Thursday, when the top Democrat on the Judiciary Committee revealed that she had referred the sexual assault allegations to federal investigators. Blasey, a research psychologist in Northern California, has accused Kavanaugh of sexually assaulting her more than 30 years ago when they were teenagers at a boozy high school party, a charge that he has categorically denied.

In a letter sent to the committee Tuesday evening, Blasey’s lawyers charged that some senators have already “made up their minds,” but she did not explicitly reject appearing before them. In an appearance on CNN, however, one of the lawyers, Lisa J. Banks, seemed to suggest that Blasey would not show up Monday.

“She’s not prepared to talk with them at a hearing on Monday,” Banks said. Even if Republicans agreed to an FBI investigation, it would take time to complete, she added. “No legitimate investigation is going to happen between now and Monday.”

Democratic leaders quickly endorsed Blasey’s position, but her resistance to coming to the committee on Monday seemed to harden the resolve of Republicans who said they gave her a chance to make her case.

“Republicans extended a hand in good faith,” said Sen. Bob Corker of Tennessee, one of the Republicans who insisted on postponing a vote until she could be heard. “If we don’t hear from both sides on Monday, let’s vote.”

Senator Charles E. Grassley of Iowa, the Judiciary Committee chairman, said he would welcome Blasey for a staff-led interview or a private hearing, if she preferred, but made clear he was sticking with the schedule for Monday.

“Dr. Ford’s testimony would reflect her personal knowledge and memory of events,” he said in a statement. “Nothing the FBI or any other investigator does would have any bearing on what Dr. Ford tells the committee, so there is no reason for any further delay.”

Trump joined other Republicans in rejecting an FBI investigation of the long-ago episode even before Blasey’s letter was sent on Tuesday evening. The bureau “said that they really don’t do that, that’s not what they do,” Trump said during a news conference. “And now they have done supposedly six background checks over the years as Judge Kavanaugh has gone beautifully up the ladder.”

In the letter to the Judiciary Committee on Tuesday evening, Blasey’s lawyers said that she has been the target of “vicious harassment and even death threats” since her name was made public on Sunday in an interview published in The Washington Post. Her email has been hacked, she has been impersonated online and she and her family have been forced to relocate out of their home, according to the lawyers, Banks and her partner, Debra S. Katz.

“While Dr. Ford’s life was being turned upside down, you and your staff scheduled a public hearing for her to testify at the same table as Judge Kavanaugh in front of two dozen US Senators on national television to relive this traumatic and harrowing incident,” the lawyers wrote to Grassley. The hearing “would include interrogation by Senators who appear to have made up their minds that she is ‘mistaken’ and ‘mixed up.’”

Blasey, who is sometimes referred to by her married name, Ford, “wants to cooperate with the committee and with law enforcement officials” but believes that a “full investigation” by the FBI would be necessary to form a non-partisan assessment before any hearing, the lawyers wrote.

Both Blasey, 51, and Kavanaugh, 53, had said on Monday morning that they were willing to come before the committee. In response, Grassley postponed a vote on the judge’s confirmation and scheduled the hearing for next week. An aide to Grassley said that the committee never intended to seat the two witnesses together at one table or even on one panel.

Democrats and Republicans spent much of Tuesday arguing over the scope and shape of what such a hearing would entail. Grassley told radio host Hugh Hewitt that Kavanaugh and Blasey would be the only witnesses, prompting pushback from top Democrats.

Another potential witness, Mark Judge, a friend of Kavanaugh’s who Blasey said was in the room when the assault occurred, told the Judiciary Committee he does not remember it. “I never saw Brett act in the manner Dr. Ford describes,” he said in a statement sent by his lawyers, adding that “I do not wish to speak publicly” about the matter.