Washington CNN  — 

Two key Republican senators who have been undecided on whether to vote to confirm Brett Kavanaugh described the FBI’s findings of an investigation into President Donald Trump’s Supreme Court nominee as a thorough report, contrasting with Democrats’ objections that the inquiry was rushed and incomplete.

Republican Sen. Susan Collins of Maine said Thursday that the FBI probe into allegations of sexual assault and inappropriate sexual behavior against Kavanaugh seems to be “very thorough” and said she would read the findings in full later in the day.

“It appears to be a very thorough investigation,” Collins, who has not yet indicated how she plans to vote on the nomination, told reporters in the Capitol.

Collins is among a handful of senators whose votes could decide the fate of the nomination. The Maine Republican – along with Republicans Sens. Jeff Flake of Arizona and Lisa Murkowski of Alaska and Democratic Joe Manchin of West Virginia – are under intense scrutiny for clues as to how they may vote on the nomination as Senate Republicans push for a final vote, which could happen as early as Saturday.

LIVE UPDATES: Senators review Brett Kavanaugh’s FBI file

Collins later clarified, “I’ve not yet finished going through all the materials.”

Flake said Thursday morning that he agreed with Collins’ pronouncement that the investigation was thorough.

When asked by CNN if he was more inclined to support Kavanaugh after leaving the staff briefing on the report, Flake responded, “we’ve seen no additional corroborating information” to the claims against Kavanaugh, and added he needs to finish reviewing the material.

Flake pushed for the FBI probe last Friday following a day full of highly-charged testimony from Kavanaugh and the woman who accused him of sexual assault, Christine Blasey Ford. Flake agreed to vote Kavanaugh’s nomination out of committee with a favorable recommendation on the condition that the FBI further investigate the allegations against Kavanaugh, a push that Collins and Murkowski publicly supported.

As for Murkowski, the Alaska senator left a closed-door briefing Thursday afternoon and said she was still reviewing the contents of the investigation. She said she wants to read the report herself when asked if she believed the investigation was thorough enough.

“I’m not wasting any daylight here,” she responded.

Murkowski said there were “readers” reading the report aloud to senators.

Among Democrats, Sen. Heidi Heitkamp of North Dakota announced Thursday afternoon that she would vote against Kavanaugh’s nomination. Heitkamp, who is up for re-election this fall in a state that went overwhelmingly for Trump in 2016, made her announcement on North Dakota station WDAY, a CNN affiliate.

“After doing my due diligence and now that the record is apparently closed, I will vote against his confirmation,” Heitkamp said in a statement, shortly thereafter.

She cited Ford’s testimony and the reaction to that as part of the influence on her decision.

“When I listened to Dr. Ford testify, I heard the voices of women I have known throughout my life who have similar stories of sexual assault and abuse,” Heitkamp said. “Countless North Dakotans and others close to me have since reached out and told me their stories of being raped or sexually assaulted – and expressed the same anguish and fear. I’m in awe of their courage, too.”

Manchin, Heitkamp and Indiana Democrat Joe Donnelly were three Democrats who voted for Trump’s first Supreme Court nominee Neil Gorsuch, a fact Heitkamp cited in her decision.

“I voted for Justice Gorsuch because I felt his legal ability and temperament qualified him to serve on the Supreme Court. Judge Kavanaugh is different,” Heitkamp said. “When considering a lifetime appointment to Supreme Court, we must evaluate the totality of the circumstances and record before us. In addition to the concerns about his past conduct, last Thursday’s hearing called into question Judge Kavanaugh’s current temperament, honesty, and impartiality.”

Donnelly announced last week he would vote against Kavanaugh.

Senate Republicans need a simple majority to clear a procedural hurdle on Friday to end debate on the nomination and advance to a confirmation vote as early as the following day.

Kavanaugh has denied all allegations against him.

CNN’s Manu Raju contributed to this report.