"I know that my tone was sharp, and I said a few things I should not have said", Kavanaugh wrote, framing his testimony as the result of his frustration with the process and his desire to clear his name after he had been accused of sexual assault - a charge which he categorically denied.
"Make no mistake, this investigation was rigged by the White House and Senate Republicans", said Sen.
Democratic Senator Dianne Feinstein noted that the Federal Bureau of Investigation did not interview Mr Kavanaugh himself or Christine Blasey Ford, a university professor from California who has accused Mr Kavanaugh of sexual assault in 1982.
But White House spokesman Raj Shah said: "What critics want is a never-ending fishing expedition into high school drinking".
Senate Judiciary Committee Chairman Chuck Grassley lashed out at reporters on Thursday, condemning what he called "bias" in the media.
Alaska Sen. Lisa Murkowski, said she was "still reviewing" her decision.
Earlier Thursday, demonstrations also took place after an FBI report looking into allegations of sexual assault against the nominee was handed over to senators, with key potential Republican holdouts indicating approval of the investigation.More news: Colorado Rockies Douse Wrigley Field In Champagne After Upsetting Cubs
Mr Trump said the protesters and "their rage-fuelled resistance is starting to backfire at a level nobody has ever seen before".
If confirmed, Kavanaugh would shift the nine-member bench markedly to the right for decades to come.
As protesters brandished signs that read "Kavanaugh lies" and "Never again" outside the steps of the supreme court, senators huddled behind closed doors in the Capitol on the other side of the street to digest the findings of an FBI investigation into the allegations against Kavanaugh.
The protesters include a loud contingent from ME, and they're calling on Susan Collins, a key Republican senator, to vote against Kavanaugh.
Three women have accused Mr Kavanaugh of sexual misconduct in separate incidents in the 1980s.
"A vote against Judge Kavanaugh tomorrow will be a vote for abusing the confirmation process and a good person, and it will be a vote for the shameful intimidation tactics that have been employed as part of an orchestrated smear campaign", he stated.
Demonstrators wait in-line to enter Hart Senate Office Building for a protest against the confirmation of Supreme Court nominee Judge Brett Kavanaugh. "We believe that all the Senate's questions have been addressed through this supplemental FBI investigation". Kavanaugh denies the allegations.
The Kavanaugh impact is much bigger for Democrats and can boost turnout in states with swing Senate and House seats in play.
Ford, a psychology professor at Palo Alto University in California, said over four hours of testimony that a drunken Kavanaugh attacked her and tried to remove her clothing at a gathering of teenagers when he was 17 years old and she was 15 in 1982.
"An FBI supplemental background investigation that did not include an interview of Dr. Christine Blasey Ford - nor the witnesses who corroborate her testimony - can not be called an investigation", her legal team said in a statement.