Republican optimism is building that Brett Kavanaugh will be voted onto the Supreme Court as party leaders claimed an FBI investigation discovered no new bombshells and two wavering senators expressed satisfaction with the probe. 

Congressmen from across the aisle spent Thursday reviewing the FBI report into claims of sexual misconduct against Mr Kavanaugh behind closed doors as the fate of Donald Trump’s choice for America’s top court hung in the balance. 

Within hours of the findings being made available on Capitol Hill some leading Republican and White House figures declared that the probe had failed to find any information which corroborated the allegations. 

However senior Democrats attacked the process, calling the investigation “incomplete” and accusing the White House of limiting its scope. One senator said it was a “cover-up” and a “complete embarrassment”.

Just a single copy of the report was produced, which was not made public.

Lawyers for two women making claims against Mr Kavanaugh – Christine Blasey Ford and Deborah Ramirez – also criticised the FBI’s probe. 

Prof Ford’s lawyer said eight people were not interviewed who could corroborate her claims, while Ms Ramirez’s lawyer said more than 20 witnesses were not contacted. 

But crucially, two key Republican senators who are yet to say how they will vote, Jeff Flake of Arizona and Susan Collins of Maine, made positive comments about the probe – taken by some as a sign they were leaning towards a ‘yes’. 

Mr Flake, who had triggered the six-day investigation by siding with Democrats last week, said: “We’ve seen no additional corroborating information.” Ms Collins said the probe “appears to be a very thorough”. 

They are two of just four senators who are yet to declare how they will vote on Mr Kavanaugh, who would be able to shape US society for generations to come if he gets the lifetime appointment on the Supreme Court. 

The Senate is split 51 Republicans to 49 Democrats and independents. That means if just two Republicans voted against Mr Kavanaugh’s confirmation it would be defeated, providing the party’s political opponents all voted against. 

Mr Flake and Ms Collins are joined by a third undecided Republican, Lisa Murkowski of Alaska. One Democrat, Joe Manchin of West Virginia, who faces re-election next month in a state won easily by Mr Trump in 2016, is also wavering. 

A second Democrat who had been seen as a doubt, Heidi Heitkamp of North Dakota, on Thursday announced she would be voting against Mr Kavanaugh’s appointment. 

An initial vote on Mr Kavanaugh’s confirmation is expected as early as 1am on Friday in Washington DC. It is a “procedural” vote which would bring debate on the nomination to an end, however it will give an indication of what senators are thinking. 

A second, final vote would need to follow. That is expected on Saturday. 

Mr Kavanaugh, a 53-year-old Yale University graduate, had been cruising to confirmation before a string of allegations from his student days surfaced late in the process. 

Prof Ford, a California academic, accused him of pinning her to a bed and groping her drunkenly at a 1982 house party when both were teenagers. Ms Ramirez accused him of exposing himself at a student party in Yale. 

Mr Kavanaugh has categorically denied both claims and said he has never sexually assaulted anyone. 

The FBI probe, triggered after Mr Kavanaugh and Prof Ford delivered emotional testimony on Capitol Hill last week, reportedly talked to nine people, including Ms Ramirez. 

Many of the other interviewees were linked to Prof Ford’s allegation. Mr Kavanaugh and Prof Ford were not interviewed.  

Chuck Grassley, the most senior Republican on the Senate committee that vets nominees, said the investigation “found no hint of misconduct” – a comment backed up by a string of the party’s senators. 

However Dianne Feinstein, the most senior Democrat on the committee, criticised the scope of the probe, saying: “What I can say is that the most notable part of this report is what’s not in it.”

In a linked development, more than 1,700 law professors signed a letter in The New York Times saying Mr Kavanaugh should not be confirmed because of the nature of his testimony last week.

Part of the letter read: "He did not display the impartiality and judicial temperament requisite to sit on the highest court of our land.” 

An estimated 3,000 protesters gathered outside the Supreme Court to protest Mr Kavanaugh’s proposed appointment, holding signs like "believe survivors" and "stop Kavanaugh". 

The confirmation battle has gripped America and is seen as a test of the where the county is in the wake of the ‘MeToo’ movement which saw a wave of sexual assault and harassment claims against powerful men. 

Sarah Sanders, the White House press secretary, rejected suggestion the FBI probe was limited by the president’s team. 

She said: “We allowed the FBI to do exactly what they do best. We haven’t micromanaged this process. We accommodated all of the Senate’s requests."

Mr Trump tweeted: