A friend of Christine Blasey Ford told FBI investigators that she felt pressured to clarify her original statement regarding an alleged sexual assault involving Supreme Court nominee Brett Kavanaugh, according to a Wall Street Journal report.
No Republicans have said they will vote against Mr Kavanaugh, although four have not committed to supporting him.
Prof Blasey Ford testified last week at a dramatic Judiciary Committee hearing that when she was 15, a drunken 17-year-old Kavanaugh pinned her down, tried to remove her clothing and covered her mouth after she screamed. She had accused him of sexual assault during a party decades ago when they were in high school. Kavanaugh himself has categorically denied the accusations against him, calling them "last minute smears" created to delay his nomination process further.
"I do not decide cases based on personal or policy preferences", he added, saying the country's top court "must never be viewed as a partisan institution".
"This is now the 7th time the FBI has investigated Judge Kavanaugh", Trump said in a tweet.
As dissent boiled on Capitol Hill, police arrested 302 protesters in the Hart Senate Office Building.
At a signal from organizers, the group began holding up signs and chanting.
Kavanaugh is a Roman Catholic who has said religion is an important part of his life.
"There is no question the Kavanaugh fight has provided a burst of energy to Republican voters at a critical time", said Brian Walsh, a Republican strategist and former staffer for the party's Senate campaign committee. "The second thing we know for sure is that there's no way anything we did would satisfy the Democrats".
That could pave the way for a confirmation vote as early as Saturday.
With Republicans holding a slim 51-49 majority in the Senate, the loss of any two of their senators would doom Kavanaugh. Democrats want a briefing from the FBI about the investigation, but Republicans declined that request.
Those not interviewed in the reopened background investigation included Kavanaugh himself and Christine Blasey Ford, who ignited the furor by alleging he'd molested her in a locked room at a 1982 high school gathering.
Democratic Sen. Tammy Duckworth of IL told reporters Thursday that time slots for reading the Federal Bureau of Investigation file are so full that senators are being told they might have to wait until Friday to read it. "Those fears have been realised".
Friday's vote is a procedural one to end the debate, and some fence-sitting senators could conceivably vote to advance Kavanaugh's nomination but still hold out their support ahead of a final confirmation roll call over the weekend.
"This process has been ruled by fear and anger and underhanded gamesmanship for too long", McConnell said.
Flake, the third Republican swing vote, said there was "no time and no place for remarks like that".
But several Democrats lit into the process, with Senator Ron Wyden branding it a "whitewash" and Senator Mazie Hirono wincing at Republican claims of comprehensiveness. "They're so swamped", she said.
Two other women have accused him of sexual misconduct during his university years.
She also claims that girls - including herself - were gang raped at these parties, but can not say whether Kavanaugh was among the attackers.
Republican Sens. Susan Collins of ME and Lisa Murkowski of Alaska have been at the center of the Kavanaugh maelstrom for months, since they expressed concerns over Kavanaugh's anti-abortion views.