Christine Blasey Ford has said US Supreme Court nominee Brett Kavanaugh sexually assaulted her as he and a friend shared “uproarious laughter” in a locked room at a 1980s high school gathering.

The 51-year-old recounted her allegations to the Senate Judiciary Committee and a riveted nation in a drama that threatens to derail Mr Kavanaugh’s Supreme Court nomination.

Her account, delivered in a soft and sometimes-halting voice, came as the judiciary panel began an extraordinary session that Republicans hope will let them salvage Mr Kavanaugh’s chances of joining the high court.

She showed no hesitancy in affirming the crucial question about the alleged incident, telling senators her certainty that Mr Kavanaugh was her attacker was “100%”.

The conservative jurist’s Senate confirmation had seemed assured until Ms Ford came forward and then other women emerged with additional allegations of sexual misconduct.

Mr Kavanaugh, now 53, has denied them all and awaited his own chance to give evidence later.

Brett Kavanaugh
Brett Kavanaugh (Jacquelyn Martin/AP)

It has become less clear that Republican leaders will be able to hold Republican senators behind President Donald Trump’s nominee.

In an election-season battle that is being waged along a polarised nation’s political and cultural fault lines, Mr Trump and most Republicans have rallied behind Mr Kavanaugh.

They have accused Ms Ford and the other women of making unproven allegations and have questioned why they had not publicly revealed them for decades.

But with televisions across the nation tuned in to the hearing – senators among those riveted to their screens – it was unclear how politicians who will ultimately decide Mr Kavanaugh’s fate will assess Ms Ford’s credibility.

Christine Blasey Ford is sworn in by Senate Judiciary Committee chairman Chuck Grassley
Christine Blasey Ford is sworn in by Senate Judiciary Committee chairman Chuck Grassley (Tom Williams/Pool Photo via AP)

Ms Ford has said Mr Kavanaugh trapped her on a bed and tried undressing her, grinding his body against her and muffling her cries with her hand.

“I believed he was going to rape me,” she said in her opening statement.

Democrats have rallied strongly behind Ms Ford.

Asked by Patrick Leahy, of Vermont, for her strongest memory of the alleged incident, Ms Ford mentioned the two boys’ “laughter – the uproarious laughter between the two and they’re having fun at my expense”.

The California psychology professor spoke carefully and deliberately during the hearing, using scientific terminology at one point to describe how a brain might remember details of events decades later.

The boys’ laughter was “indelible in the hippocampus”, she said.

Ms Ford has said Kavanaugh friend Mark Judge was also in the room.

Mr Judge has said he does not remember the alleged incident and has declined to appear before the panel.

Christine Blasey Ford before the Senate Judiciary Committee on Capitol Hill in Washington
Christine Blasey Ford before the Senate Judiciary Committee on Capitol Hill in Washington (Andrew Harnik/AP)

Ms Ford told the top committee Democrat, California Senator Dianne Feinstein, that she had “agonised daily” over coming forward about the alleged decades-old attack.

She said she feared the personal consequences would be akin to “jumping in front of a train”.

In fact, both she and Mr Kavanaugh have received death threats.

When Ms Feinstein asked her how she could be sure that Mr Kavanaugh was the alleged attacker, Ms Ford said: “The same way I’m sure I’m talking to you right now.”

Later, she told Senator Dick Durbin that her certainty was “100%”.

The judiciary panel’s 11 Republicans – all men – let Rachel Mitchell, a veteran sex crimes prosecutor from Arizona, ask their questions.

She began by expressing sympathy for Ms Ford, who had said she was “terrified” to give evidence, saying: “I just wanted to let you know, I’m very sorry. That’s not right.”

Ms Mitchell led Ms Ford through a detailed recollection of the events she says occurred on the day of the alleged incident.

Rachel Mitchell
Rachel Mitchell (Andrew Harnik/AP)

But under the committee’s procedures, the career prosecutor was limited to five minutes at a time, interspersed between Democrats’ questions, creating a choppy effect as she tried piecing together the story.

Before Ms Ford began, committee chairman Chuck Grassley defended the Republicans’ handling of the confirmation proceedings so far.

Ms Feinstein criticised Republicans who have rejected Democratic demands to slow Mr Kavanaugh’s confirmation process and let the FBI investigate all the allegations, saying: “What I don’t understand is the rush to judgment.”

Mr Kavanaugh and Ms Ford are the only witnesses invited to give evidence before the panel.

But the conservative jurist is facing allegations of sexual misconduct from other women as well, forcing Republican leaders to struggle to keep support for him from eroding.

Mr Grassley complained that lawyers for other accusers have not provided information to his panel, and said: “The committee can’t do an investigation if attorneys are stonewalling.”

Chuck Grassley
Chuck Grassley (Win McNamee/Pool Photo via AP)

Republicans acknowledged that much was riding on Mr Kavanaugh’s performance.

Even Mr Trump, who fiercely defends his nominee, said he would be watching and was “open to changing my mind”.

Republicans are pushing to seat Mr Kavanaugh before the November midterms, when Senate control could fall to the Democrats and a replacement Trump nominee could have even greater difficulty.

Mr Kavanaugh’s ascendance to the high court could help lock in a conservative majority for a generation, shaping dozens of rulings on abortion, regulation, the environment and more.

Republicans also risk rejection by female voters in November if they are seen as not fully respecting women and their allegations.

Ms Ford finished her evidence about four hours after the hearing began.