Perhaps the most damaging new revelation in the report, according to multiple people familiar with it, is a previously unreported text message in which Peter Strzok, a key investigator on both the Clinton email case and the investigation of Russian Federation and the Trump campaign, assured an FBI lawyer in August 2016 that "we'll stop" Trump from making it to the White House.
"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 Federal Bureau of Investigation and department norms, the decisions negatively impacted the perception of the Federal Bureau of Investigation and the department as fair administrators of justice", Horowitz said in his summary.
Attorney General Jeff Sessions justified the firing of James Comey and offered that more terminations might be the outcome of the Investigator General's report set to be released Thursday. The investigation expanded to touch on an array of politically sensitive decisions by officials including Comey and former Attorney General Loretta Lynch.
While some of their messages were anti-Trump, others took aim at lawmakers such as U.S. Senator Bernie Sanders, whom Clinton defeated for the Democratic presidential nomination. When Horowitz announced the review in January 2017, he said it would address accusations that Peter Kadzik, the former head of legislative affairs at DOJ, gave "non-public information" to Clinton campaign chairman John Podesta, after reports on stolen emails from WikiLeaks revealed Kadzik sent a "heads up" about a congressional hearing where another Justice official was likely to be questioned about Clinton's email use. But it will mark the most definitive accounting of the email probe to date, looking at - among other things - whether "certain underlying investigative decisions were based on improper considerations".
The report did hammer Comey's handling of the Clinton investigation, but did not assert any political "bias".
Over 17 months in the making, the report is expected to walk through a sequence of key events leading up to the 2016 election. "We'll stop it", Strzok fired-back.
Lynch - after a controversial private meeting with former President Bill Clinton - did not formally recuse herself from the case, but she had announced that she would go along with whatever Comey recommended.
Page has since left the FBI and Strozk, who was assigned but then removed from Special Counsel Robert Mueller's investigation of Russia's interference in 2016 election, remains with the agency. Comey informed Congress of the emails October 28, 2016.
Comey said he faced the tough choice of speaking out or concealing the information.
On Wednesday, Attorney General Jeff Sessions said the report could prompt more firings.