WASHINGTON — In a stinging rebuke, the Justice Department watchdog declared Thursday that former FBI Director James Comey was “insubordinate” in his handling of the Hillary Clinton email investigation in the explosive final months of the 2016 presidential campaign. But it also found there was no evidence that Comey’s or the department’s final conclusions were motivated by political bias toward either candidate.

President Donald Trump and his supporters had looked to the much-anticipated report to provide a fresh line of attack against Comey and the FBI as Trump claims that a politically tainted bureau tried to undermine his campaign and — through the later Russia investigation — his presidency.

Clinton and her supporters, on the other hand, have long complained that she was the one whose election chances were torpedoed by Comey’s investigation announcements about her email practices, in the summer and then shortly before the election.

Comey, whom Trump fired shortly after taking office, bore the brunt of much criticism in the report, but not for political favoritism.

The inspector general concluded that the FBI director, who announced in the summer of 2016 that Clinton had been “extremely careless” with classified material but would not be charged with any crime, departed from normal Justice Department protocol numerous times.

But it also said, “We found no evidence that the conclusions by the prosecutors were affected by bias or other improper considerations; rather, we determined that they were based on the prosecutors’ assessment of the facts, the law and past department practice.”

The conclusions were contained in a 500-page report that documents in painstaking detail one of the most consequential investigations in modern FBI history and reveals how the bureau, which for decades has endeavored to stand apart from politics, came to be entangled in the 2016 presidential election.

Trump supporters quickly focused on the report’s recounting of anti-Trump text messages from two FBI officials who worked the Clinton probe and later the Russia case, including one in which an agent says, “We’ll stop it” with regard to a possible Trump victory. The report suggests that text from Peter Strzok, who was later dropped from Mueller’s team, “implies a willingness to take official action to impact the presidential candidate’s electoral prospects.”