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.