A Justice Department watchdog report has found that former FBI director James Comey was insubordinate and "deviated" from procedures in his handling of the probe into Hillary Clinton's email server but did not do so because of political bias.
The inspector general's report also found that Comey had damaged the image of impartiality of various law-enforcement agencies.
"While we did not find that these decisions were the result of political bias on Comey's part, we nevertheless concluded that by departing so clearly and dramatically from FBI and department norms, the decisions negatively impacted the perception of the FBI and the department as fair administrators of justice," Inspector General Michael Horowitz wrote in the report.
The release of the full report later Thursday is expected to re-ignite the simmering dispute over Comey's actions during the presidential 2016 election.
The report had been expected to offer new ammunition to both parties in the high-stakes dispute over the Clinton email investigation, which has played a central role in the election and in Robert Mueller's investigation into whether President Donald Trump obstructed justice by firing Comey last May.
Trump initially claimed that he fired Comey because of his handling of the email probe. Two days after the firing, Trump told NBC's Lester Holt that the Russia investigation was on his mind when he made the decision. Last month, the president wrote in a post on Twitter: "I never fired James Comey because of Russia!"
The president has predicted the IG's report would have "so many horrible things to tell."
Clinton has blamed her 2016 defeat on Comey's actions the month before the election.
Comey has been criticized for publicly announcing his decision to re-open the FBI's investigation in the days before the election.
Justice Department policies bar investigators from interfering in elections.
The conclusions of Thursday's report also touched on the anti-Trump text messages exchanged by Peter Strzok and Lisa Page, investigators who worked on Mueller's probe. Trump had claimed the text messages, in which the two called the president an "idiot," were a "bombshell," and he has used them to cast doubt on the Russia probe, which he has repeatedly called a "witch hunt."
"We did not find documentary or testimonial evidence that improper considerations, including political bias, directly affected the specific investigative actions we reviewed," the inspector general wrote.
Their conduct did, however, "cast a cloud over the entire FBI investigation," according to the report.
Mueller removed Strzok from the Russia investigation once he became aware of the text messages. Page left Mueller's staff before the text messages were uncovered. Strzok, who was reportedly involved in an extramarital affair with Page, had previously played a key role in the Clinton email investigation.
The report said Comey's lack of communication with then-Attorney General Loretta Lynch during the investigation was "troubling."
It found that Comey did not speak directly and substantively with the attorney general in advance of his July press conference in which he called Clinton's actions "extremely careless," or his Oct. 28 letter to Congress announcing his re-opening of the investigation.
"We found it extraordinary that, in advance of two such consequential decisions, the FBI director decided that the best course of conduct was to not speak directly and substantively with the attorney general about how best to navigate those decisions," the report said.
Lynch had said she would respect Comey's recommendations on the Clinton investigation after it became public that Lynch had briefly met with former President Bill Clinton in June 2016 while the two were waiting on the same airport tarmac in Phoenix. Lynch has said the conversation consisted of small talk.
Lynch never formally recused herself, saying that her legal advisors did not recommend that she do so.
The IG investigation, opened in January 2017, has been heavily politicized, with some suggesting it would provide fodder to both Republicans and Democrats.
"I imagine it will be one of those things that both sides will look at and be like, see, I told you so," Donald Trump Jr., the president's son, said on "Fox & Friends" on Thursday morning.
"The stark conclusion we draw after reviewing this report is that the FBI's actions helped Donald Trump become President," two top House Democrats said after reviewing the report Thursday.
"As we warned before the election, Director Comey had a double-standard," Reps. Jerry Nadler of New York and Elijah Cummings of Maryland said in the statement. "He spoke publicly about the Clinton investigation while keeping secret from the American people the investigation of Donald Trump and Russia."
Rep. Bob Goodlatte, R-VA, chair of the House Judiciary Committee, said in a statement following the report's release that it "confirms that former Secretary of State Hillary Clinton received special treatment."
The report had faced delays in publication, earning the ire of the president and some Republican lawmakers, who expressed concern that the report was being modified.
"We're a little disappointed in that this has been delayed another week, and my experience with this is a lot of time the lawyers get a hold of it and they start to water down the report," House Intelligence Committee Chairman Devin Nunes, R-Calif., said earlier this month.
Horowitz said in April his report would be out the following month. He later pushed back the release date to Thursday. He is expected to testify to Congress about the report Monday.