President Donald Trump has effectively called the accuser of his Supreme Court nominee Brett Kavanaugh a liar, saying it’s hard for him to “imagine that anything happened”.

Mr Trump was referring to the sexual assault allegation brought by professor Christine Blasey Ford, who alleges Mr Kavanaugh sexually assaulted her 35 years ago at a party when both were teenagers.

Professor Ford wants the FBI to investigate her allegation that she was sexually assaulted by Mr Trump’s US Supreme Court nominee before she testifies at a Senate Judiciary Committee hearing on Monday (local time), her lawyers have written in a letter.

“If she shows up and makes a credible showing, that will be very interesting and we’ll have to make a decision,” President Trump said. “But I can only say this, he is such an outstanding man. Very hard for me to imagine that anything happened.”

Mr Trump ramped up his defence of his nominee, praising him as “an extraordinary man” with “an unblemished record,” and adding that what he is experiencing is “unfair”.

When asked on Thursday morning (AEST) if Professor Ford’s allegation would disqualify Mr Kavanaugh if proved true, Mr Trump declined to answer directly, saying only he needed to hear her story first.

“I would really want to see her. I would want to see what she has to say,” he told reporters before flying to the Carolinas to survey the aftermath of Hurricane Florence.

Her lawyers wrote that Professor Ford, who is now a college professor in California, wants to cooperate with the panel. But in the days since she publicly accused Mr Kavanaugh of the sexual assault at a party 35 years ago, she has been the target of “vicious harassment and even death threats”. Her family has relocated, they said.

An FBI investigation “should be the first step in addressing the allegations,” the lawyers wrote in the letter, which was obtained by The Associated Press.

President Trump has repeatedly reacted to the allegation by backing Mr Kavanaugh and even showing sympathy for the embattled Supreme Court nominee.

However, Senate Republicans and Democrats have been fighting over who should testify at a high-stakes hearing on the allegation which is due to occur just six weeks before major congressional elections.

Democrats have said they wanted more time for the FBI to investigate – and more witnesses besides Mr Kavanaugh and Professor Ford, hoping to avoid what would turn into merely a “he-said-she-said” moment.

Mr Kavanaugh is Mr Trump’s choice to serve on the Supreme Court. Photo: Getty

Those witnesses would include Mr Kavanaugh’s high school friend Mark Judge, who Professor Ford said was in the room when she was assaulted, but Mr Judge said no.

Mr Kavanaugh has denied Professor Ford’s allegation, and Mr Judge says he doesn’t remember any such incident.

The lawyers for Professor Ford predicted the hearing, as now scheduled, “would include interrogation by senators who appear to have made up their minds” that she is “mistaken” and mixed up.

‘I don’t have an Attorney-General’

Meanwhile Mr Trump has stepped up his attacks on his Attorney-General Jeff Sessions, saying: “I don’t have an attorney-general”.

Mr Trump, in a Hill.TV interview released on Wednesday (local time), said that he was “so sad over Jeff Sessions”, who he had repeatedly denounced for recusing himself from the Russia investigation.

“He was the first Senator that endorsed me. And he wanted to be Attorney-General, and I didn’t see it,” Mr Trump said in the Oval Office interview.

“And then he went through the nominating process and he did very poorly. I mean, he was mixed up and confused, and people that worked with him for, you know, a long time in the Senate were not nice to him, but he was giving very confusing answers. Answers that should have been easily answered.”

The President softened his stance slightly when talking to reporters on the White House lawn hours after the interview’s publication, saying: “I’m disappointed in the Attorney-General for numerous reasons, but we have an Attorney-General.”

Mr Trump has repeatedly asserted that Mr Sessions, a former US senator from Alabama, did not need to step away from the Russia probe, a move the President believes in part led to the appointment of special counsel Robert Mueller, who is investigating contacts between Trump campaign officials and Russians

-with agencies