"While we found no evidence that Comey's statement was the result of bias or an effort to influence the election, we did not find his justifications for issuing the statement to be reasonable or persuasive".
Mr. Trump also took aim at Mr. Comey - who he fired in May 2017.
Both sides of the partisan divide found something to trumpet in the report.
In October 2016, less than two weeks before the election, Comey sent members of Congress a letter disclosing that a probe into Clinton's emails was being reopened after new emails were discovered, a disclosure Clinton contends contributed to her surprise defeat by Trump.
"FBI Agent Peter Strzok, who headed the Clinton & Russia investigations, texted to his lover Lisa Page, in the IG Report, that "we'll stop" candidate Trump from becoming President", Trump said in a tweet.
U.S. President Donald Trump speaks to reporters on the North Lawn of the White House on Friday in Washington.
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.
The Justice Department's internal watchdog branded Comey as insubordinate for repeatedly breaking with Justice Department protocol in his handling of the email probe involving Democrat Hillary Clinton.
I think what happened here is that I used instant message and chat like it was my home, ' said Agent 1.
"I do not agree with all of the inspector-general's conclusions, but I respect the work of his office and salute its professionalism. That's the nature of hard decisions; they don't allow for certainty". It's focused on a specific set of events back in 2016, and a small number of Federal Bureau of Investigation employees connected with those events.
'Trump's not ever going to become president, right?'
Strzok replied: "No. No he won't. No he won't. We'll stop it".
The inspector general's probe focused on decisions made by Comey, at key moments during the campaign, to go public with the FBI's findings, sidestepping then-Attorney General Loretta Lynch.