The Justice Department watchdog excoriated the FBI for relying upon British ex-spy Christopher Steele's dossier in obtaining Foreign Intelligence Surveillance Act warrants to monitor onetime Trump campaign adviser Carter Page.

Inspector General Michael Horowitz, who released a report on Monday showing his findings regarding allegations of surveillance abuses, also found the FISA process was significantly flawed and marred by serious mistakes and missteps, but determined that the initiation of the Trump-Russia investigation itself crossed the low threshold to be properly predicated and was not influenced by political bias as some of President Trump's allies have alleged.

Horowitz's findings provide Trump and his allies fodder in their criticism of FBI and DOJ officials who investigated him, while Democrats, who have defended the FBI's actions, are engaged in an impeachment effort examining whether the president abused his office.

Attorney General William Barr seized on Horowitz's findings, declaring in a lengthy statement that the report shows the FBI's counterintelligence investigation was conducted in an inappropriate manner given the evidence the bureau had on hand.

"The Inspector General’s report now makes clear that the FBI launched an intrusive investigation of a U.S. presidential campaign on the thinnest of suspicions that, in my view, were insufficient to justify the steps taken," Barr said in a statement.

In stark contrast, House Judiciary Committee Chairman Jerry Nadler, the Democrat who is taking a leading role in the impeachment proceedings, said Horowitz's report "debunks conspiracy theories" and "affirms that DOJ and FBI had an authorized purpose to conduct temporary surveillance as part of the investigation.”

The inspector general "identified at least 17 significant errors or omissions in the Carter Page FISA applications and many errors in the Woods Procedures" which guide the FBI's FISA process, according to the 476-page report.

"These errors and omissions resulted from case agents providing wrong or incomplete information to the National Security Division’s Office of Intelligence and failing to flag important issues for discussion,” Horowitz said.

But Horowitz’s team “did not find documentary or testimonial evidence that political bias or improper motivation influenced the decisions to open the four individual investigations” into Page, former Trump campaign foreign policy adviser George Papadopoulos, former national security adviser Mike Flynn, and former Trump campaign manager Paul Manafort in the summer of 2016.

FISA warrants were not obtained against Papadopoulos, Flynn, or Manafort.

The FBI's counterintelligence investigation, dubbed "Crossfire Hurricane, was initiated in late July 2016 and was later wrapped into special counsel Robert Mueller's investigation into Russian election interference. It effectively began after Australian diplomat Alexander Downer met with Papadopoulos at London's Kensington Wine Rooms in May 2016, and Papadopoulos allegedly said the Russians had damaging information on Hillary Clinton. Two months later, after WikiLeaks published stolen emails from the Democratic National Committee, the Australians informed the U.S. about what Papadopoulos told Downer.

Horowitz said in his report that the genesis of the Crossfire Hurricane inquiry was unrelated to the dossier, which some Trump allies have alleged, although the FBI had already obtained Trump-related information from Steele before the investigaiton began. Horowitz said the predicate for the investigation was "sufficient" because of a "first-hand account from a friendly foreign government employee of a conversation with Papadopoulos."

Papadopoulos, who pleaded guilty in 2017 to making false statements to the FBI and served 12 days in prison last year, said the man who informed him about the Russian dirt on Clinton was mysterious Maltese academic Joseph Mifsud. Mueller said Mifsud had ties to the Russian government, but some Republicans claim he had ties to Western intelligence.

Horowitz began looking into possible government surveillance abuses in March 2018 after a memo from Republicans leading the House Intelligence Committee alleged the Justice Department and FBI misled the Foreign Intelligence Surveillance Court, which approved four warrants targeting Page, by not adequately disclosing the dossier's Democratic benefactors and his bias against Trump.

House Intelligence Committee Democrats argued in a rebuttal memo that the FISA applications also contained evidence against Page that was not in the dossier and the FBI "met the rigor, transparency, and evidentiary basis needed to meet FISA's probable cause requirement."

The inspector general team's two-year investigation concluded in mid-September after reviewing over one million records and conducting over 170 interviews involving more than 100 witnesses, and in recent weeks his work has been shrouded in speculation amid a back-and-forth between the DOJ and inspector general related to classification of the document.

The Page FISA applications required approval from top members of the FBI and the Justice Department; and targets of Horowitz's investigation included the approvers of the four applications and renewals: former FBI Director James Comey; former Deputy Attorney General Sally Yates; Dana Boente, the only signatory in active government service and currently Trump’s top lawyer at the FBI; then-FBI Deputy Director Andrew McCabe; and then-Deputy Attorney General Rod Rosenstein, who appointed former FBI Director Mueller to be special counsel the month before.

Yet all the high-level signatories did not act with a political bias against Trump, Horowitz found, and the DOJ watchdog is known to have criminally referred only one FBI lawyer, Kevin Clinesmith, who has since left the bureau, for altering an email that was used by officials as they prepared an application renewal to present before the Foreign Intelligence Surveillance Court.

“That so many basic and fundamental errors were made by three separate, hand-picked teams on one of the most sensitive FBI investigations that was briefed to the highest levels within the FBI, and that FBI officials expected would eventually be subjected to close scrutiny, raised significant questions regarding the FBI chain of command's management and supervision of the FISA process,” Horowitz said.

Horowitz made nine recommendations to the DOJ and FBI, including putting in place proper procedures for DOJ leadership to obtain all relevant and accurate evidence needed to prepare FISA applications and renewal applications, such as confidential human source information, and asking the FBI to review the performance of all the employees in the chain of command responsible for the Page FISA investigation and take appropriate disciplinary action.

Barr said in a statement on Monday that FBI Director Christopher Wray is "dismayed" about the handling of these FISA applications. As seen in an appendix at the bottom of Horowitz's report, Wray ordered the FBI to take more than 40 corrective steps to address the the inspector general's recommendations.

Horowitz's team examined the FISA application and three renewals beginning in October 2016 to surveil Page. The applications relied on the unverified dossier compiled by Steele, who was hired by opposition research firm Fusion GPS and funded by Democrats.

The 412 pages of redacted FISA documents released in 2018 show the DOJ and the FBI made extensive use of Steele’s unverified dossier, which he put together in 2016 at the behest of Fusion GPS. The Clinton campaign hired the firm through Marc Elias of the Perkins Coie law firm and was briefed about Steele's findings throughout the race.

The DOJ inspector general said when he launched the investigation last year at the behest of then-Attorney General Jeff Sessions he would “examine the Justice Department’s and the FBI’s compliance with legal requirements" related to FISA filings against Page and review the DOJ’s and the FBI’s dealings with Steele.

Officials such as Deputy Assistant Secretary of State Kathleen Kavalec knew by October 2016 portions of Steele’s dossier were inaccurate. And State Department officials such as Jonathan Winer and Victoria Nuland were involved in spreading Steele's information within the U.S. government.

Many members of the media also received info from the Steele dossier at the behest of Fusion GPS co-founder Glenn Simpson.

There was speculation by Barr, the National Security Council's former Russia expert Fiona Hill, and former intelligence officials that the dossier may have contained Russian disinformation, though Steele claimed there's no way he was duped by the Kremlin.

The Steele dossier's central thesis was "a well-developed conspiracy of co-operation" between the Trump campaign and Russia, but Mueller didn't agree. Although Mueller concluded the Russians interfered in the 2016 presidential election, the investigation did not establish the Kremlin and Trump's campaign criminally conspired. Mueller’s report also seemed to shoot down at least one of Steele’s biggest claims — that Trump lawyer Michael Cohen met with foreign hackers in Prague.

U.S. Attorney John Durham, at the behest of Barr, launched his own broader inquiry earlier this year into the origins of the Trump-Russia investigation, and this fall it was reported that Durham's administrative review had shifted to a criminal investigation.

Horowitz is scheduled to testify about his FISA report at 10 a.m. on Wednesday before the Senate Judiciary Committee.