McCabe’s lawyer, former DOJ inspector general Michael R. Bromwich, ‏tweeted in response: “Thank you for providing even more material for the defamation suit we are actively considering filing against you and your colleagues. Stay tuned.”

The report, written by Inspector General Michael Horowitz, details the investigation that US Attorney General Jeff Sessions cited when he fired McCabe hours before he was set to retire and receive his full pension.

It says McCabe “lacked candour” in conversations with Comey, who was then FBI director, and other officials about his role in providing information to the reporter on an investigation into the Clinton Foundation.

The report notes that McCabe, as deputy director, had full authority to authorise sharing information with the media, and says that he permitted subordinates to do so in this case to correct a false narrative that he had tried to stymie an FBI probe into the foundation. 

The conversation “was done to protect the institutional reputation of the FBI as a non-political and professional investigative agency, and therefore was squarely within the public interest exception to the FBI’s prohibition on sharing sensitive material”, the document finds.  

However, the inspector general also found that McCabe didn’t inform then-FBI Director James Comey that he had authorised disclosure of the information to a Wall Street Journal reporter. The inspector general “concluded that McCabe’s disclosure of the existence of an ongoing investigation in this manner violated the FBI’s and the Department’s media policy and constituted misconduct,“ according to a copy of the report.

Trump had accused McCabe of bias, and the president’s critics said McCabe was fired from the FBI as part of a Republican effort to discredit a federal investigation into purported ties between Russia and the Trump presidential campaign.

“The rush to termination was nothing short of extraordinary,” Bromwich said in an interview.

McCabe, who has argued he was being singled out because he was a witness into whether Trump tried to obstruct the federal probe, said in a statement on Friday he was authorised to share that information with reporters and had not intentionally misled anyone.

He said that when he believed his answers to the inspector general were misunderstood, he returned and tried to correct them. 

“McCabe had no motive to lie or mislead about media contacts he had the authority to direct,” Bromwich said in an emailed statement.

The inspector general’s report does not square with the Republican narrative of the FBI as a politically biased institution, as the story - which was published on October 30 last year - contained derogatory information about Clinton and her foundation. 

But its conclusion may also be hard for Democrats to embrace, given its harshly critical suggestion that McCabe had put his personal reputation above the interests of the FBI.

Separately, the inspector general sent a letter to members of the Senate Judiciary Committee saying that the full report is expected to be issued in May. The office had previously said the report would be released this month. 

A broader report coming from the inspector general is expected to address a number of politically sensitive issues, including how the FBI handled its investigation into Hillary Clinton’s use of a private email server when she was secretary of state.

It will also look at the early stages of the FBI’s investigation into whether Trump or any of his associates helped Russia interfere in the 2016 election.  

Republican critics have already seized on revelations that two FBI officials who worked on the Russia investigation, Peter Strzok and Lisa Page, exchanged text messages that were sharply critical of Trump. 

But the agents also criticised Clinton in their texts, and it’s unclear whether their work was swayed by their personal views. Mueller removed Strzok from the Russia inquiry after the texts were discovered, and Page had already left his team.