The chances of securing a 2016 surveillance warrant for a Trump campaign aide were “50/50” without the controversial anti-Trump “dossier,” according to testimony in newly confirmed congressional transcripts.

The October testimony from senior FBI lawyer Sally Moyer to House investigators appers to underscore how critical the dossier -- funded by the Democratic Party and Clinton campaign -- was in obtaining the Foreign Intelligence Surveillance Act (FISA) warrant, and appears to conflict with Democratic assertions that the dossier played a limited role in the process.

Asked whether the FBI would have been able to establish probable cause if the application “did not have the Christopher Steele information in it,” Moyer responded: "So I think it's a close call, like 50/50, 51/49. I really think it's a close call."

Moyer was responding to a series of questions about the opposition research by British ex-spy Christopher Steele, who worked for Fusion GPS, and how the unverified and salacious dossier was used to secure the warrant for campaign aide Carter Page in October 2016 -- less than one month before the presidential election.

Moyer spoke to investigators with the House Oversight and Judiciary Committees, in a closed-door transcribed interview last fall, when Republicans held the House. The witness transcripts are not public and remain under review by the FBI and Justice Department.

Moyer went on to say that some officials felt the surveillance-warrant application was strong and sufficient without the dossier.

"With it, I don't think it's a close call. With it, I think that clearly meets the probable cause standard," Moyer testified.

Question: "Right. But without it there are those that felt it did meet a probable cause standard?"

Moyer: "Yes."

Question: "And those that didn't, it was still a close call."

Moyer: "Yes."

Question: “Okay. So it was a close call by those that looked at it or had a discussion about it and maybe some that felt it was sufficient without it?”

Moyer: “Correct.”

Moyer is a key witness as a lead attorney for the FBI’s 2016 Clinton email and Russia investigations. Her testimony about the dossier’s importance to the surveillance warrant application appears consistent with that of former FBI Deputy Director Andrew McCabe.

According to a memo from Republicans on the House Intelligence Committee in February 2018 about the Page warrant, "McCabe testified before the Committee in December 2017 that no surveillance warrant would have been sought from the [Foreign Intelligence Surveillance Court] without the Steele dossier information."

By contrast, a dueling FISA memo drafted by intelligence committee Democrats found "DOJ cited multiple sources to support the case for surveilling Page -- but made only narrow use of information from Steele's sources about Page's specific activities in 2016, chiefly his suspected July 2016 meeting in Moscow with Russian officials."

The publicly available surveillance warrant for Carter Page, released by the Justice Department, is heavily redacted.

During his closed-door testimony in December, according to now-public transcripts, former FBI Director James Comey appeared vague when pressed by a House Republican on Moyer's earlier testimony.

In his responses, Comey identified Moyer as "a lawyer in the General Counsel's Office."

FORMER TOP FBI LAWYER REVEALS INVOLVEMENT IN CARTER PAGE FISA WARRANT

Rep. John Ratcliffe, R-Texas: “I'll represent to you that she testified that the FISA court -- it was 49-51, maybe 50-50, that the FISA court would have approved the warrant without the Steele dossier. If I represent that to you, does that cause you concern that the court was relying on a document that was largely unverified and minimally corroborated?"

Comey: "No. Because it asked me to assume the truth of the last part of your question, and I don't know that to be the case. "

During her October testimony, Moyer was also pressed by lawmakers on whether she was "aware of any evidence that President Obama ordered any investigative activity that was biased in favor of Secretary Clinton or biased against President Trump?"

Moyer answered, "No."

On allegations that the Russia investigation was politically motivated, Moyer was asked, ”Are you aware of any conspiracy against Donald Trump or the Trump campaign involving anyone from the FBI or the Department of Justice or President Obama?” Moyer responded, “No.”

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Moyer also stated there was no White House interference on the 2016 investigations involving the presidential candidates. Moyer was asked, “Are you aware of any evidence that President Obama ordered any investigative activity that was biased in favor of Secretary Clinton or biased against President Trump?” She again responded, “No.”

Fox News reached out to the FBI for additional comment or context, and the bureau declined to comment.