Critics of the woman who has accused Supreme Court nominee Brett Kavanaugh of sexual assault are stepping up their attack on her.

The Federal Bureau of Investigation is probing allegations made by Christine Blasey Ford that she was attacked in the 1980s by US President Donald Trump's pick to fill a seat on the bench of the country's highest court.

Since she came forward, the United States has been engulfed in chaos that led to a Senate hearing in which Mr Kavanaugh regularly erupted in anger, reports news.com.au.

Dr Ford has been praised for her bravery in coming forward and hailed a hero for survivors of sexual assault.

But those disputing her testimony say there are countless holes in her story and that her account of the alleged attack by Mr Kavanaugh and a friend, Mark Judge, at a high school party, is not credible.

'A FLIMSY CASE'

Arizona sex crimes prosecutor Rachel Mitchell was hired by Republicans to ask questions of Mr Kavanaugh and Dr Ford during hearings — a move Democrats attacked because neither were on trial.

Nonetheless, in a memo sent by Ms Mitchell, she said it was her view that no "reasonable prosecutor would bring this case based on the evidence before the Committee".

NBC News reports that she wrote that her "bottom line" was that "a 'he said, she said' case is incredibly difficult to prove".

"But this case is even weaker than that," Ms Mitchell wrote. "Dr Ford identified other witnesses to the event, and those witnesses either refuted her allegations or failed to corroborate them."

Ms Mitchell wrote that in Dr Ford's previous accounts of the alleged incident — particularly in sessions with marriage and individual therapists in 2012 and 2013 — she struggled to identify Mr Kavanaugh as the assailant by name.

FORMER PARTNER'S CLAIMS

Fox News reported it has obtained a written declaration from an unnamed ex-boyfriend of Dr Ford, who insisted she never mentioned Mr Kavanaugh.

They were in a relationship from 1992 to 1998, the man claimed in the statement, which also disputed several of her other claims.

Prior to testifying before the Senate, Dr Ford said she did not want to appear because she was afraid to fly and was suffered PTSD from the alleged assault that made her anxious in confined spaces. She also she was uncomfortable in rooms without two doors.

"I was hoping to avoid getting on an airplane. But I eventually was able to get up the gumption with the help of some friends and get on the plane," Dr Ford testified.

In his declaration, the ex-boyfriend said Dr Ford never expressed a fear of flying and was once a passenger in a propeller plane.

He also claimed they shared a small apartment with only one front door.

Senate Judiciary Committee Chairman Chuck Grassley cited the man's declaration and insisted lawyers for Dr Ford provide notes from her therapist.

REAL ESTATE RECORDS EMERGE

Dr Ford said she first disclosed the alleged sexual assault in 2012 during therapy sessions with her husband, after they began to fight over her insistence they install a second front door.

The additional entry was an "escape route" that she required due to anxiety and claustrophobia she suffered as a result of the alleged assault.

However, real estate records have emerged showing the door was installed four years before the therapy sessions in 2008.

It was part of extensive renovation works on the couple's California home, which also included a new bathroom.

And health care records reportedly obtained surrounding the 2012 therapy sessions detail that Dr Ford worked from a home office, which Republicans say was the reason for the second door.

POLYGRAPH TEST CLAIMS

Dr Ford sat for a polygraph lie detector test in August and answered questions about the alleged attack, which she passed.

She told the Senate hearing that she had "never" had "any discussions with anyone … on how to take a polygraph". She also denied giving "any tips or advice to anyone who was looking to take a polygraph test".

But her ex-boyfriend's declaration said Dr Ford had helped a friend prepare for a polygraph test for a job interview and "explained in detail what to expect, how polygraphs worked and helped (her) become familiar and less nervous about the exam," using her background in psychology.

The statement has fuelled attacks from Republicans on Dr Ford, who claim she has produced no credible evidence to prevent Mr Kavanaugh from proceeding with his confirmation hearing.

INVESTIGATION ALMOST DONE

Fox News cites a source as saying the FBI is preparing to conclude its investigation into misconduct allegations against Mr Kavanaugh within the next day.

However, Reuters reports that several witnesses who say they have information about the case have tried and failed to speak with FBI investigators.

The FBI has already interviewed Mr Judge, who denied any memory of such an incident, as well as at least three other people with information about the allegations.

They also probed claims by a second accuser, Deborah Ramirez. Ms Ramirez claimed Mr Kavanaugh exposed himself to her when they both attended Yale University.

"It is inconceivable that the FBI could conduct a thorough investigation of Dr Ford's allegations without interviewing her, Judge Kavanaugh, or the witnesses we have identified in our letters to you," Dr Ford's lawyers said in a letter to FBI Director Christopher Wray.

BIZARRE CLINTON CONSPIRACY

Mr Kavanaugh has claimed the assault allegations are part of a conspiracy of revenge orchestrated by Hillary and Bill Clinton.

Lynne Brookes, a former classmate of Kavanaugh, alleges he was misleading about the extent of his drinking at Yale.

“There is no doubt in my mind that while at Yale, he was a big partier, often drank to excess and there had to be a number of nights where he does not remember.” pic.twitter.com/YTnWRlXoyC

— Cuomo Prime Time (@CuomoPrimeTime) September 28, 2018

As a young lawyer, he spent considerable time on the Kenneth Starr team investigating Bill Clinton's affair with White House intern Monica Lewinsky.

Democrats have called the comment a breathtaking breach of judicial impartiality that should be disqualifying on its own, while Republicans have defended the tenor of Mr Kavanaugh's remarks, saying he had every right to be upset.

At an event on Tuesday, Ms Clinton scoffed: "Boy, I'll tell you, they give us a lot of credit."

"This whole two-week effort has been a calculated and orchestrated political hit," Mr Kavanaugh testified.