Former FBI Director James Comey seriously violated his bureau’s norms in its controversial probe of former Secretary of State Hillary Clinton’s use of a private server to conduct official U.S. diplomatic business, but Department of Justice Inspector General (DOJIG) Michael Horowitz said in a much-anticipated report that political bias was not involved.

The 568-page report said DOJIG investigators were hampered in their work by thousands of emails and text messages exchanged among five senior FBI executives, including former counterintelligence chief Peter Strozk and his lover, FBI lawyer Lisa Page.

“These messages reflected political opinions in support of former Secretary Clinton and against her then political opponent, Donald Trump. Some of these text messages and instant messages mixed political commentary with discussions about the [email] investigation, and raised concerns that political bias may have impacted investigative decisions,” the report said.

“In particular, we were concerned about text messages exchanged by FBI Deputy Assistant Director Peter Strzok and Lisa Page, Special Counsel to the Deputy Director, that potentially indicated or created the appearance that investigative decisions were impacted by bias or improper considerations.

“As we describe in Chapter 12 of our report, most of the text messages raising such questions pertained to the Russia investigation, which was not a part of this review. Nonetheless, the suggestion in certain Russia-related text messages in August 2016 that Strzok might be willing to take official action to impact presidential candidate Trump’s electoral prospects caused us to question the earlier [email] investigative decisions in which Strzok was involved, and whether he took specific actions in the [email] investigation based on his political views.

“[W]e found that Strzok was not the sole decision-maker for any of the specific [email] investigative decisions we examined in that chapter. We further found evidence that in some instances Strzok and Page advocated for more aggressive investigative measures in the [email].”

As a result, the report said, “Our review did not find evidence to connect the political views expressed in these messages to the specific investigative decisions that we reviewed; rather, consistent with the analytic approach described above, we found that these specific decisions were the result of discretionary judgments made during the course of an investigation by the [email] agents and prosecutors and that these judgment calls were not unreasonable.”

The report’s conclusion on the issue of political bias in the FBI probe are likely to anger Trump and Republican leaders in Congress and elsewhere who have argued for months that Comey and his close colleagues manipulated their investigation to protect Clinton and defeat Trump.

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The conclusions are also likely to stun some of Horowitz’s strongest supporters because he has a sterling reputation as a nonpolitical straight shooter and somebody who is not afraid to recommend prosecution based on facts.

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Horowitz will testify June 18 before the Senate Judiciary Committee about the report, and that hearing is almost certain to feature fireworks between Republicans and Democrats trying to spin the DOJIG’s findings and in pressing him to justify his conclusion that political bias was not a factor in the FBI’s Clinton email investigation.

Horowitz’ probe was prompted by an avalanche of criticism of the FBI’s handling of Clinton’s private email system. Despite saying hundreds of highly classified documents were jeopardized by Clinton’s actions and those of her closest aides and that it was likely the private server was compromised by foreign intelligence agencies and hackers, Comey announced in July 2016 that he would not recommend prosecution.

He briefly reopened the investigation just before the election, when hundreds of thousands more of Clinton’s private server emails were found on a laptop used by her deputy chief of staff Huma Abedin and her husband, disgraced former New York Rep. Anthony Weiner. But shortly thereafter, Comey said nothing was found on the laptop that justified revising his July conclusion.

Comey’s July statement edits. The report documented multiple edits made to Comey’s draft in the weeks before his July statement effectively sparing Clinton from prosecution:

“Comey’s initial draft statement, which he shared with FBI senior leadership on May 2, criticized Clinton’s handling of classified information as ‘grossly negligent,’ but concluded that ‘no reasonable prosecutor’ would bring a case based on the facts developed in the [email] investigation.

Related: New FBI Emails Wreck Official Clinton Email Timeline

“Over the course of the next 2 months, Comey’s draft statement underwent various language changes, including the following:

• The description of Clinton’s handling of classified information was changed from ‘grossly negligent’ to ‘extremely careless;’

• A statement that the sheer volume of information classified as Secret supported an inference of gross negligence was removed and replaced with a statement that the classified information they discovered was ‘especially concerning because all of these emails were housed on servers not supported by full-time staff;’

• A statement that the FBI assessed that it was ‘reasonably likely’ that hostile actors gained access to Clinton’s private email server was changed to ‘possible.’ The statement also acknowledged that the FBI investigation and its forensic analysis did not find evidence that Clinton’s email server systems were compromised; and,

• A paragraph summarizing the factors that led the FBI to assess that it was possible that hostile actors accessed Clinton’s server was added, and at one point referenced Clinton’s use of her private email for an exchange with then-President Barack Obama while in the territory of a foreign adversary. This reference later was changed to ‘another senior government official,’ and ultimately was omitted.

“Each version of the statement criticized Clinton’s handling of classified information. Comey told us that he included criticism of former Secretary Clinton’s uncharged conduct because ‘unusual transparency … was necessary for an unprecedented situation,’ and that such transparency ‘was the best chance we had of having the American people have confidence that the justice system works.”

The edits will draw fireworks in the Senate hearing for two reasons:

First, “gross negligence” is the standard for prosecuting individuals under the Espionage Act, thus removing that reference all but protected Clinton from a potentially catastrophic blow to her presidential campaign.

The report agreed with Comey’s conclusion that there was insufficient evidence to justify prosecuting Clinton for gross negligence because the DOJIG decided the statute “likely required a state of mind that was ‘so gross as to almost suggest deliberate intention,’ criminally reckless, or ‘something that falls just short of being willful,’ as well as evidence that the individuals who sent emails containing classified information ‘knowingly’ included or transferred such information onto unclassified systems. The [email investigative] team concluded that such proof was lacking.”

There are multiple former U.S. attorneys in the Republican congressional caucus who will scoff at the report’s logic on the gross negligence issue.

IG report confirms Obama knew. Second and perhaps most important among many significant points, the report confirms Obama knew Clinton was using a private email system to conduct official U.S. diplomatic business.

Soon after the Clinton email scandal first exploded with a March 2, 2015, New York Times story, that publication’s Michael Shear reported on March 7, 2015, that “President Obama said Saturday that he had learned only last week that Hillary Rodham Clinton used a private email system for her official correspondence while she was secretary of state.”

Shear’s report was based on a televised interview of Obama by CBS correspondent Bill Plante. Shear noted that “in the portion of the interview that was released, Mr. Obama did not address how he could have avoided noticing that Mrs. Clinton was sending emails from a ‘’ address throughout the years she served in his administration.”

Reporters bribing FBI agents? The report uncovered what it described as “numerous FBI employees, at all levels of the organization and with no official reason to be in contact with the media, who were nevertheless in frequent contact with reporters.” The report includes an appendix documenting such communications in April and May of 2016 and October 2016.

“We have profound concerns about the volume and extent of unauthorized media contacts by FBI personnel that we have uncovered during our review. In addition, we identified instances where FBI employees improperly received benefits from reporters, including tickets to sporting events, golfing outings, drinks and meals, and admittance to nonpublic social events,” the report said.

A separate report on those relationships and gifts will be released at a later date, the IG said.

Senior editor Mark Tapscott can be reached at [email protected]. Follow him on Twitter.