The report says that McCabe "lacked candour" on four occasions when talking to a Wall Street Journal reporter a year ago about the FBI's investigation into a foundation run by Bill and Hillary Clinton, and also neglected to tell his then-boss, James Comey, that he had authorised the disclosure of the information.
The inspector general also concluded that Mr. McCabe's disclosure of the existence of the ongoing investigation in the manner described in the report violated media policy of the F.B.I. and Justice Department and constituted misconduct. However, the way McCabe did it broke the rules: his methods were "designed to advance his personal interests at the expense of Department leadership" and the disclosed information "was clearly not within the public interest exception".
Attorney General Jeff Sessions fired McCabe on March 16 - two days short of his retirement and receiving a full pension.
On Friday, Trump and his allies celebrated the report, even before its public release. "He LIED! LIED! LIED!"
Michael Bromwich, a lawyer for McCabe, said in a statement that McCabe's treatment was "far more harsh and far less fair than he deserved", and that the inspector general's report "utterly failed to support the decision to terminate Mr. McCabe". The office had previously said the report would be released in April.
The 35-page inspector general report goes into detail in arguing McCabe intentionally misled internal FBI and inspector general investigators about whether he had authorized the disclosure of an August 2016 phone conversation regarding the FBI's Clinton Foundation investigation to The Wall Street Journal.
The rush to termination was nothing short of extraordinary - a process that normally takes many months, if not longer, was completed in 23 days.
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McCabe, who served as Deputy Director for almost two years, was sacked last month.
McCabe responded to the firing by charging it was part of a larger effort from the Trump administration to discredit the FBI and special counsel Robert Mueller's investigation.
The statement was in response to a Trump tweet that said McCabe "LIED!" The account of the August 12 McCabe-PADAG call, and other information regarding the handling of the CF Investigation, was included in the October 30 WSJ article.
Bromwich criticized the inspector general investigation for leaning too much on the "admittedly vague and uncertain" recollections of Comey about what McCabe told him. "House Republicans will nearly certainly try to use this report to fuel their efforts to distract from the abuses of power by this Administration and to undermine the Department of Justice". "McCabe was sacked in disgrace for misconduct and lying about it".
"Andy's 19 years of experience, combined with his vision, judgment and ability to communicate, make him a ideal fit for this job", Comey said in a statement at the time.
But Republicans say the report shows McCabe's firing was justified.
The report says McCabe twice told investigators that he didn't know anything about how the information got out.
Republican critics have already seized on revelations that two FBI officials who worked on the Russian Federation investigation, Peter Strzok and Lisa Page, exchanged text messages that were sharply critical of Trump. But she also disclosed that the Clinton Foundation, the Clinton family charity, was under investigation.