"They have destroyed the lives of people that were great people, that are still great people", Trump said.
"We also identified what we believe is an absence of sufficient policies to ensure appropriate Department oversight of significant investigative decisions that could affect constitutionally protected activity", Horowitz will say, according to his prepared remarks as released by the committee before the hearing.
Attorney General Bill Barr's criticism of Monday's inspector general report was unexpected, Justice Department watchdog Michael Horowitz told Senators on Wednesday.
Yet Horowitz also repeatedly noted under questioning from Democrats that he had not found that the FBI had targeted Trump for investigation for political reasons.
When the FBI opened its investigation - known as "Crossfire Hurricane" - into possible coordination between members of President Donald Trump's campaign and Russian Federation, it had both an "authorized purpose" and an "articulable factual basis", the IG report found.
Republican lawmakers will virtually actually query Mr. Horowitz about supplies that investigators relied on to use for the courtroom order, specifically a file of unverified, salacious details about Mr. Trump compiled by a British former spy, Christopher Steele, whose analysis was funded by Democrats.
To determine which campaign officials had Russian connections, the Federal Bureau of Investigation used various methods listed among its "least intrusive" measures, such as open-source searches, the report said.
The FBI then used confidential human sources - a "permitted" but more intrusive technique - to "interact and consensually record conversations" with Papadopoulous and Page. "It doesn't mean though that the entire Russian Federation investigation was therefore illegitimate".
That was a "pretext", Horowitz said, to collect information that might be relevant for the investigation.
In an interview Tuesday, Attorney General William Barr blasted Horowitz's report, telling NBC News that "I think our nation was turned on its head for three years based on a completely bogus narrative that was largely fanned and hyped by a completely irresponsible press".
"I would hate to lose the ability of the FISA court to operate at a time probably when we need it the most", Graham said.
Wray, the FBI director, announced the bureau would implement 40 changes, particularly when it comes to how it handles informants and applications to the Foreign Intelligence Surveillance Court. He invoked notorious former FBI Director J. Edgar Hoover, he read the damning anti-Trump text messages between FBI agent Peter Strzok and lawyer Lisa Page that prompted Horowitz to look into the origins of the investigation, and he said he may no longer support the Foreign Intelligence Surveillance Act (FISA) Court without serious reforms.