The draft of Horowitz's wide-ranging report specifically called out Comey for ignoring objections from the Justice Department when he disclosed in a letter to Congress just days before the 2016 presidential election that FBI agents had reopened the Clinton probe, according to sources. Clinton has said that letter doomed her campaign.

Before Comey sent the letter to Congress, at least one senior Justice Department official told the FBI that publicizing the bombshell move so close to an election would violate longstanding department policy, and it would ignore federal guidelines prohibiting the disclosure of information related to an ongoing investigation, ABC News was told.

In an interview in April, ABC News Chief Anchor George Stephanopoulos asked Comey: "If Attorney General Lynch had ordered you not to send the letter, would you have sent it?"

"No," Comey responded. "I believe in the chain of command."

But in backing Trump's ultimate decision to fire Comey last year, Deputy Attorney General Rod Rosenstein slammed Comey's letter to Congress and said it "was wrong" for Comey "to usurp the Attorney General's authority" when he announced in July 2016 that the FBI would not be filing charges against Clinton or her aides.

"It is not the function of the Director to make such an announcement," Rosenstein said in a letter to Trump recommending Comey be fired. "At most, the Director should have said the FBI had completed its investigation and presented its findings to federal prosecutors."

Horowitz's draft report cited Comey for failing to consult with Lynch and other senior Justice Department officials before making his announcement on national TV.