(CNN) -- Senators Thursday morning are reviewing the supplemental FBI background file for Brett Kavanaugh, which could determine the fate of embattled Supreme Court nominee.
The review comes amid pressure from Senate Majority Leader Mitch McConnell and President Donald Trump to confirm Kavanaugh in the face of sexual assault allegations, which he has denied.
The White House and Republican lawmakers said the additional interviews from the FBI show no corroboration of the allegations against Kavanaugh and plan to go ahead with a key procedural vote Friday.
The FBI, however, is not tasked with drawing conclusions, and only provided the White House with summaries of the interviews it conducted.
The most consequential conclusions will be made by four key swing votes on Kavanaugh's nomination: Republican Sens. Lisa Murkowski of Alaska, Jeff Flake of Arizona, Susan Collins of Maine and Democratic Sen. Joe Manchin of West Virginia.
Collins Thursday morning did not say how she would vote but said of the report that, "it appears to be a very thorough investigation."
Flake, who worked last week to force the FBI probe, told CNN that "we've seen no additional corroborating information" regarding the allegations.
Democrats claim otherwise, saying that the FBI failed to interview potential witnesses willing to come forward or who could corroborate charges against Kavanaugh.
"It looks to be a product of an incomplete investigation that was limited, perhaps by the White House," Sen. Dianne Feinstein, D-California, told reporters.
The week since Kavanaugh and Christine Blasey Ford testified before the Judiciary Committee has heightened tensions and mistrust between Democrats and Republicans over the nomination, which can cement a decades-long conservative majority on the Supreme Court. The FBI did not interview Ford.
Trump believes that confirming Kavanaugh under such circumstances could also boost Republican turnout in the midterm elections, but it also seems certain to further alienate women voters in the #MeToo era in a way that could help Democrats.
"The harsh and unfair treatment of Judge Brett Kavanaugh is having an incredible upward impact on voters. The PEOPLE get it far better than the politicians," Trump tweeted Thursday morning. "Most importantly, this great life cannot be ruined by mean & despicable Democrats and totally uncorroborated allegations!"
"We feel very confident that when the senators have an opportunity to review this material, as they're just beginning to right now, that they're going to be comfortable voting for Judge Kavanaugh," White House spokesman Raj Shah said on CNN's "New Day."
Grassley said he will vote for Kavanaugh.
"I trust that the career agents of the FBI have done their work independent of political or partisan considerations. That's exactly what senators from both sides asked for. Now it's up to senators to fulfill their constitutional duty and make a judgment," he said in a statement. "No one is on trial and the Senate is not a courtroom. But our nation's tradition of fairness still applies. A presumption of innocence is how the American justice system works, and it should remain our guidepost in the Senate. Abandoning that principle would cut a sad path for the Senate as an institution."
The file was delivered to the committee in a sealed box at 2:30 a.m. ET, according to a committee source, who also told CNN that it was placed in a vault that already holds Kavanaugh's six other background investigation reports.
Senators and nine staff members will be the only people who can review the full report. There is one copy in a secure room on Capitol Hill. Phones are not allowed and any notes taken must be left in the room. Democrats and Republicans will alternate control of the room and document every hour.
A further FBI investigation into Kavanaugh's background was put into motion last week when Flake voted to move Kavanaugh's nomination out of the committee but called for the FBI to further investigate Ford's claims.