By Kristine Phillips and Kevin Johnson, USA TODAY–

Justice Department Inspector General Michael Horowitz will testify Wednesday about his findings that the FBI was legally justified in launching its investigation into Russia’s interference in the 2016 presidential election.

In a voluminous report, the Justice Department’s watchdog debunked claims by President Donald Trump and his allies that political bias played a role in the FBI’s decision to investigate members of the Trump campaign for possible coordination with Russia. But the inspector general also found that the investigation’s early stages, specifically the controversial surveillance of a former Trump campaign aide, was riddled with mistakes.

Horowitz will testify before the Senate Judiciary Committee, chaired by Sen. Lindsey Graham, R-S.C., a fierce ally of Trump.

Democrats, Republicans and the president have each declared victories after Horowitz released his report Monday.

Democrats said the report, the product of a nearly two-year-long review, discredited conspiracy theories fanned by Trump and Republicans about how the Russia investigation began. Republicans, citing serious errors Horowitz identified, said the report back their claim that the bureau’s top law enforcement officials abused their power.

The president, now facing impeachment charges of abuse of power and obstruction of Congress, reiterated his claims that the Russia investigation was an attempt to overthrow the government.

Horowitz examined the FBI’s decision in summer 2016 to launch Crossfire Hurricane, which later became known as the Russia probe. Specifically, the inspector general looked at the FBI’s applications to wiretap Page, as well as the bureau’s decision to investigate other campaign aides and Trump associates.

The inspector general also examined the FBI’s relationship with Christopher Steele, a former British intelligence officer who was hired by Fusion GPS, a research firm working for then-Democratic presidential rival Hillary Clinton’s campaign. Steele, who was an FBI source for years, authored the infamous “dossier” alleging ties between Trump and Russia.

The FBI relied on Steele’s research about Page’s activities in Moscow to convince judges to approve and renew warrant applications to wiretap Page. But the report said the research “played no role” in the broader decision to open the Russia probe, which began months before the FBI started monitoring Page.

Horowitz identified 17 inaccuracies across three surveillance applications that effectively inflated the justification to monitor Page. Among the most common errors were the omission of important information, including some that contradicted investigators’ suspicions, the report said.

For example, in its wiretap applications, the FBI didn’t note Page’s denials that he had talked to allies of Russian President Vladimir Putin about lifting sanctions against Russia and giving the Trump campaign damaging information about Clinton. And the FBI omitted information about Steele: that he had previously exercised “poor judgement,” that he had a history of pursuing people “with political risk but no intelligence value,” and that he did not want Trump to become president, the report said.

“Indeed, a significant amount of the information gathered during these operations was inconsistent with the Steele election reporting and should have been provided to Department attorneys, but was not,” the report said.

Horowitz: DOJ inspector general, set to release major report on FBI’s Russia investigation, spent years prosecuting corrupt officials

FBI Director Christoper Wray said the bureau “accepts” the report’s findings. He said in a letter to Horowitz that the FBI will make “concrete changes” so that its surveillance process is “more stringent and less susceptible to mistake or inaccuracy.”

The president on Tuesday attacked Wray after the FBI director disputed Trump’s claims that federal authorities mounted a “coup” attempt against him.

“With that kind of attitude,” Wray “will never be able to fix the FBI, which is badly broken despite having some of the greatest men & women working there!” Trump tweeted.

Hours after Trump’s broadside, Attorney General William Barr said he supported the FBI director, though he maintained that the Russia investigation was not justified, despite the findings of the inspector general.

Barr, who is overseeing a parallel inquiry into the origins of the Russia probe, said the mistakes in the surveillance of Page suggest the FBI acted in “bad faith.”

This article originally appeared on USA TODAY: DOJ watchdog Michael Horowitz testifies on his findings before Senate Judiciary Committee