Three wavering Republican senators lambasted U.S. President Donald Trump on Wednesday for mocking a woman who has claimed Brett Kavanaugh sexually assaulted her in the 1980s, underscoring the risks of assailing the Supreme Court nominee's three accusers as Senate support teeters.

The blowback to Trump's scoffing at Christine Blasey Ford came as lawmakers awaited results of a revived FBI background check, expected imminently, on accusations of sexual misconduct by Kavanaugh in high school and college.

Senate majority leader Mitch McConnell, a Republican from Kentucky, has said the chamber will vote on Kavanaugh this week, and the conservative jurist's fate is in the hands of a handful of undecided Republican and Democratic senators.

At a political rally in Mississippi on Tuesday night, Trump mimicked Ford's responses at a Senate judiciary committee hearing last week at which she recounted Kavanaugh's alleged attack on her when both were in high school. The audience laughed as Trump, at times inaccurately, recounted what he described as holes in her testimony.

"I had one beer — that's the only thing I remember," Trump said.

Watch Trump criticize Christine Blasey Ford's testimony:

The U.S. president has mocked Brett Kavanaugh's accuser, who testified against the Supreme Court nominee last week 0:44

On NBC's Today show on Wednesday, Sen. Jeff Flake, a Republican from Arizona, said ridiculing "something this sensitive at a political rally is just not right."

"I wish he hadn't done it. It's kind of appalling."

Separately, Sen. Susan Collins, a Republican from Maine, told reporters "the president's comments were just plain wrong" and Republican Sen. Lisa Murkowski of Alaska said they were "wholly inappropriate and in my view unacceptable."

Republican Senators Lisa Murkowski, left, Jeff Flake, centre and Susan Collins separately criticized Trump for mocking Ford. (Associated Press/Getty Images)

Republican Sen. Chuck Grassley, chairman of the Senate Judiciary committee, said in a tweet that people can "decide who to believe" but everyone should stop the "personal attacks" against Ford, Kavanaugh and their families.

Republican lawmakers expressed concern that Trump's comments could make it harder to win over wavering colleagues whose votes will likely prove pivotal to Kavanaugh's chances.

"All of us need to keep in mind there's a few people that are on the fence right now. And right now, that's sort of where our focus needs to be," said Sen. Bob Corker of Tennessee, who has traded barbs with Trump and will retire at year's end.

Speaking at an event hosted by The Atlantic magazine, Republican Sen. Lindsey Graham of South Carolina said he "didn't particularly like" the president's remarks, with the Trump ally adding: "I would tell him, knock it off. You're not helping."

All eyes on key senators

Trump's aggressive criticism of Ford seems to reflect the sentiments of some of his conservative supporters. But it raises questions about how such words will affect five senators — all moderates — whose votes on Kavanaugh will be decisive.

Flake has clashed repeatedly with Trump over his behaviour and is retiring at the end of the year. Collins has criticized Trump at times as well but not as often as Flake.

Democrats Joe Manchin of West Virginia and Heidi Heitkamp of North Dakota have yet to declare their positions on Kavanaugh.

The attention now shifts to Democratic Senators Joe Manchin, left, and Heidi Heitkamp, who have yet to declare their positions on Kavanaugh. (Getty Images)

Trump's comments about Ford reflected a growing frustration among some in the White House, and by the president, that her story has not received the same level of scrutiny as Kavanaugh's, said a person close to the process who was not authorized to speak publicly.

In response, White House spokesperson Sarah Sanders disputed claims that what Trump said was "anything other than the president stating facts, facts laid out in [special prosecutor Rachel Mitchell's] memo that she put forward to the Senate."

"Certainly, the testimony by Dr. Ford was compelling, but you can't make this decision based on emotion. It has to be based on fact. They have to determine what the facts are of this case," Sanders said at Wednesday's press briefing.

Christine Blasey Ford, who testified before the judiciary committee in Washington on Sept. 27, alleges Kavanaugh sexually assaulted her in 1982 when they were in high school. (Win McNamee/Associated Press)

Democrats contend the investigation has not been expanded to sufficient potential witnesses. Senate minority leader Chuck Schumer, a Democrat from New York, has said he wants senators to receive an FBI briefing on its findings at least 24 hours before the chamber takes its first procedural vote on Kavanaugh. Republicans have given no sign of assenting to that.

"This entire process has been a disgrace and the only reason that it's been that way is because Senate Democrats didn't do this the way that it should have been done and they circumvented the entire system," Sanders said.

"They have undermined our entire judicial branch with the inappropriateness of which they have conducted themselves."

FBI probe due to wrap up

McConnell told reporters Tuesday that "I can tell you with certainty" that the FBI report will be finished and the Senate will vote this week, though he didn't specify when. Underscoring the Republican effort to vote on Kavanaugh quickly — and end the chances for fresh allegations to emerge — he said "it shouldn't take long" for lawmakers to read the report.

The FBI has finished an interview with Chris Garrett, a high school friend of Kavanaugh. Garrett's lawyer, William Sullivan, said Garrett has voluntarily co-operated with the FBI's reopened background check, but he declined to comment further.

Garrett is at least the fifth person known to have been interviewed since last Friday, when the White House directed the FBI to look again into the allegations.

Others interviewed include Mark Judge, who Ford has said was in the bedroom where, she alleges, a drunken Kavanaugh sexually attacked her at a 1982 high school gathering. Also interviewed were two other people Ford said were present but in a different room: Patrick (P.J.) Smyth and Leland Keyser. Judge, Smyth and Keyser say they don't recall the incident described by Ford.

Kavanaugh has denied the accusations by Ford and Deborah Ramirez, who says he exposed himself to her during a college party, and Julie Swetnick, who has alleged she was victimized at a party attended by Kavanaugh and his friends.

Besides Trump, Senate Republicans also began to aim credibility questions at Ford.

In a letter Tuesday night, the chairman of the Senate judiciary committee pressed Ford to turn over more information to support her claim and accused her lawyers of "withholding material evidence." Grassley repeated his request for notes from Ford's therapy sessions, details of her communications with the Washington Post and any recordings of her taking a lie detector test.

Brett Kavanaugh, shown testifying Sept. 27 before the judiciary committee, has denied allegations of sexual misconduct. (Gabriella Demczuk/Reuters)

The senator said he was requesting the recordings because the committee has obtained a letter that "raises specific concerns" about the reliability of Ford's polygraph test. In the statement, a man who says he is Ford's former boyfriend says he saw Ford, a psychology professor, coach a friend on how to be less nervous during a polygraph examination.

If true, the claim could contradict testimony Ford gave last week, when she told senators she had never given tips or advice to anyone taking a lie detector test.

A representative of Ford's legal team had no immediate comment.