The Senate is set to vote Friday morning on the first step to confirming Judge Brett Kavanaugh to the Supreme Court following the release of an FBI report on allegations of sexual misconduct by Kavanaugh.

Senators had one day to review a confidential supplemental background check into Kavanaugh's behavior in the early-to-mid 1980s when he was in high school and college. The closely guarded collection of interviews is celebrated by Republican leaders as concrete proof that Kavanaugh did not harass or abuse women. Democrats say the interviews, which they originally requested, are incomplete and inconclusive.

The FBI report has done little to alleviate a bitter partisan fight over Kavanaugh's nomination. Senate Majority Leader Mitch McConnell, R-Ky., says the Senate will proceed anyway on a Friday procedural vote that could pave the way for a final confirmation vote on Saturday.

"What we know for sure is the FBI report did not corroborate any of the allegations against Judge Kavanaugh," McConnell said at a press conference. "The second thing we know for sure is that there's no way anything we did would satisfy the Democrats."

Kavanaugh took an unusual step to boost his nomination Thursday evening, writing an op-ed in the Wall Street Journal expressing regret for the heated tone of his testimony before the Senate Judiciary Committee last week, including comments decrying Democratic attacks that was seen by some wavering senators as too partisan.

"I was very emotional last Thursday, more so than I have ever been. I might have been too emotional at times. I know that my tone was sharp, and I said a few things I should not have said," Kavanaugh wrote.

McConnell needs 51 votes to clear the procedural hurdle on Friday. Republicans have enough votes to meet that bar on their own, but only if they win the support of Sens. Lisa Murkowski, R-Alaska, Jeff Flake, R-Ariz., and Susan Collins, R-Maine, who have withheld judgement while the FBI completed its work.

All three spent hours in a secure room in the basement of the Capitol Thursday reviewing the roughly 45 pages of FBI interviews. Collins and Flake both say the investigation was thorough, but neither would say if they are now prepared to vote to confirm Kavanaugh.

Flake forced Republicans to launch the additional investigation last week after a tense negotiation with Senate Judiciary Committee Democrats. Flake spent a large portion of the afternoon reviewing the FBI work and said he saw no new evidence to corroborate any of the claims against Kavanaugh, which Flake had previously indicated would mean he will vote to confirm.

Democrats saw something very different in the report. Several criticized Republicans for limiting the FBI investigation to just nine interviews. They said the process ignored many potential witnesses, including Christine Blasey Ford, the woman who first accused Kavanaugh of sexually assaulting her at a high school party in the 1980's.

The FBI also did not interview Kavanaugh.

Senate Minority Leader Chuck Schumer said those issues raised serious doubts about Kavanaugh and his qualifications.

"Judge Kavanaugh stated at his hearing that the individuals at the incident involving Dr. Ford refuted her version of events," Schumer said. "From their own public statements, we knew that to be false, and nothing in this report changes that."

Similar concerns moved Sen. Heidi Heitkamp, D-N.D., to announce Thursday that she would oppose Kavanaugh. Heitkamp is one of the most vulnerable Democrats on the ballot in November and has seen her poll numbers slip in recent weeks. She's running for re-election in a state president Trump won in 2016 by more than 35 points.

Heitkamp said she was troubled by Kavanaugh's aggressive appearance before the Senate Judiciary committee and the message his confirmation would send to women and girls across the country.

"When considering a lifetime appointment to Supreme Court, we must evaluate the totality of the circumstances and record before us," Heitkamp said in a statement. "In addition to the concerns about his past conduct, last Thursday's hearing called into question Judge Kavanaugh's current temperament, honesty, and impartiality."

Her opposition leaves Sen. Joe Manchin, D-W.Va., as the only undecided Democrat. He is also in a tough reelection campaign and was silent on Kavanaugh in the days leading up to the vote.

The nomination now hangs on the decisions of Collins, Murkowski, Flake and Manchin.

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