The report finds those tactics complied with existing FBI policy, but the review contains withering criticism of the pre-eminent law enforcement agency for “basic, fundamental and serious errors” handling of the surveillance applications for campaign adviser Carter Page.

“We are deeply concerned that so many basic and fundamental errors were made by three separate, hand-picked investigative teams; on one of the most sensitive FBI investigations; after the matter had been briefed to the highest levels within the FBI; even though the information sought through the use of FISA authority related so closely to an ongoing presidential campaign; and even though those involved with the investigation knew that their actions were likely to be subjected to close scrutiny,” Horowitz wrote.

“We believe this circumstance reflects a failure not just but those who prepared the FISA applications, but also by the managers and supervisors in the Crossfire Hurricane chain of command, including FBI senior officials who were briefed as the investigation progressed,” the inspector general added.

President Donald Trump welcomed the report, which he said exposed deep corruption at the FBI.

“It’s a disgrace what’s happened with the things that were done to our country...it’s incredible, far worse than what I ever thought possible,” Trump said during a White House meeting shortly after the review emerged. “They fabricated evidence and they lied to the courts. … This was an attempted overthrow and a lot of people were in on it, and they got caught.”

Attorney General Bill Barr endorsed Horowitz’s critique of the FBI’s handling of the surveillance process, but rejected the inspector general’s conclusion that the FBI had an adequate “predicate” for the decision to launch the investigation into the Trump campaign in July 2016.

“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. “It is also clear that, from its inception, the evidence produced by the investigation was consistently exculpatory. Nevertheless, the investigation and surveillance was pushed forward for the duration of the campaign and deep into President Trump’s administration.”

Barr blasted the FBI’s actions in 2016 as “a clear abuse of the FISA process.”

In addition, a career federal prosecutor Barr tapped to review other issues related to the Trump-Russia probe—U.S. Attorney for Connecticut John Durham—said in an unusual statement Monday that his ongoing inquiry raises doubts about Horowitz’s conclusion that the FBI had an adequate basis for opening its probe into Trump campaign aides.

“Our investigation has included developing information from other persons and entities, both in the U.S. and outside of the U.S.,” Durham said. “Based on the evidence collected to date, and while our investigation is ongoing, last month we advised the Inspector General that we do not agree with some of the report’s conclusions as to predication and how the FBI case was opened.”

Congressional Democrats welcomed Horowitz’s findings about the opening of the Trump-Russia probe and downplayed the wide array of flaws the inspector general found the FBI’s handling of the highly sensitive inquiry.

“The IG’s report shows that the investigation Special Counsel Mueller took over was not politically motivated and that officials acted appropriately in opening the investigation,” House Judiciary Committee Chairman Jerrold Nadler and House Oversight Committee Chairwoman Carolyn Maloney said in a joint statement. “While the IG identified some problems with the FISA applications by lower level individuals, the IG ‘did not find documentary or testimonial evidence of intentional misconduct.’ The report affirms that DOJ and FBI had an authorized purpose to conduct temporary surveillance as part of the investigation.

However, Nadler and Maloney appeared to express concern that the inspector general’s findings would fuel claims by Trump’s supporters that his campaign was unfairly targeted by investigators in 2016.

“The president, his defenders in Congress, and right-wing media will continue to prop up these conspiracy theories to deflect from the President’s misconduct, but we will not be distracted by their baseless allegations,” the Democratic lawmakers said. “President Trump is a continuing threat to our elections and the sanctity of our democracy.”

Former FBI Director James Comey hailed the watchdog report, painting it as a forceful refutation of Trump’s claims that FBI officials engaged in “treason” by deliberately interfering in the electoral process.

“There was no illegal wiretapping, there were no informants inserted into the campaign, there was no ‘spying’ on the Trump campaign,” Comey said in a Washington Post op-ed.. “Although it took two years, the truth is finally out.”

Comey also swung at Barr, writing: “Those who smeared the FBI are due for an accounting. In particular, Attorney General William P. Barr owes the institution he leads, and the American people, an acknowledgment of the truth.”

Horowitz was cautious in stating his findings about the motivations of key players in the investigation, perhaps because of the prior disclosure of text messages between a key FBI agent overseeing the Russia probe, Peter Strzok and an FBI attorney, Lisa Page, expressing disdain for Trump and hope that Hillary Clinton would win the election.

The inspector general report says investigators “did not find documentary or testimonial evidence that political bias or improper motivation” impacted the FBI’s decision to open the investigation or to pursue surveillance of Carter Page. But the review stops short of ruling out such bias and says explanations by current and former officials of various failures in the process were perplexing and inadequate.

“We … did not receive satisfactory explanations for the errors or problems we identified,” the report says.

The report also details examples of pro-Trump bias within the FBI, including an official hailing Trump’s election and writing “shit just got real” in a message to colleagues.

Horowitz exonerates Justice Department officials involved in the surveillance requests, saying they were unaware of inconsistent or inaccurate information from the FBI and an intelligence agency who had worked with Page.

However, the inspector general said the errors and omissions were so troubling that he is launching a broad audit of FISA applications to see if other submissions to that court in unrelated investigations contain similar flaws.

He also recommended changes to Justice Department policies to require advance approval from prosecutors before launching an investigation into a political campaign and before deploying FBI informants in such a probe.

The report’s release Monday followed last-minute, mixed signals from President Donald Trump and his allies about whether the review would office much in the way of blockbuster revelations that the probe was tainted by politics.

The review took on a larger-than-life quality over the past year-and-a-half, with some Trump supporters predicting that it would show that Trump and his advisers were the victims of a politically motivated vendetta by FBI agents and Obama appointees intent on undermining Trump’s upstart presidential bid and the early days of his presidency.

Former officials said Horowitz’s report contradicted Trump’s narrative by concluding that the FBI and Justice Department’s investigative interest in Russian ties to the Trump campaign was legitimate and that — by and large — the investigation was handled professionally.

But the watchdog report harshly criticized some aspects of the inquiry, including the FBI’s vetting of a so-called “dossier” of accurate, inaccurate and unconfirmed information on alleged ties between Russia and candidate Trump’s coterie.

Republicans say the FBI relied too heavily on the dossier prepared by former British intelligence officer Christopher Steele, didn’t do enough to verify it and was not explicit enough with judges about the fact that Steele’s work was funded by Hillary Clinton’s presidential campaign and the Democratic Party. The surveillance applications did contain a page-long footnote that said Steele was funded by someone who appeared intent on finding “information that could be used to discredit [Trump’s] campaign.”

Horowitz’s review found that the applications submitted to federal judges exaggerated the significance and scope of Steele’s prior work with the FBI on an investigation into corruption in international soccer. The inspector general’s team also found a total of 17 inaccuracies or omissions in the surveillance applications filed with the court, despite DOJ policies calling for every application to be thoroughly scrubbed and substantiated with detailed documentation.

In several instances, the FBI’s own documentation clearly contradicted information relayed to judges, the report found. As details about the investigation began to spill out publicly in 2017, the FBI also failed to flag to the court publicly available information that undercut the bureau’s conclusion that Steele did not directly leak information that led to a key news story revealing the U.S. government’s scrutiny of Page.

Horowitz’s report does not attempt to assess whether the omissions and inaccuracies would have led the judges to deny the surveillance, if properly included.

Horowitz’s team had been intensely focused on gauging Steele’s credibility as a source for the bureau. Steele cooperated with the inspector general investigation throughout the summer, and sat for more than 16 hours of interviews in London and by Skype, according to people familiar with his participation in the inquiry. He was also able to review the portions of the report that mention him prior to its release, as is standard.

But Steele was told on Sunday by a staffer in the IG’s office that details about him had been newly declassified and would be included in the report, according to two sources with direct knowledge of the conversation. Steele was not given a chance to review the newly declassified material and was not briefed on its content prior to the report’s release.

Trump, meanwhile, has repeatedly sought to drum up interest in Horowitz’s review, stoking expectations about it even on the eve of its release.

“I.G. report out tomorrow. That will be the big story!” the president wrote on Twitter Sunday.

However, in recent days, Trump also seemed to prepare his supporters for the possibility that Horowitz’s report might not be the game-changer some Trump backers have been anticipating, with the most significant revelations still to come from Durham.

“I'm looking forward to seeing the IG report,” Trump told reporters at the White House on Saturday. “And I look forward very much to seeing what happens with the Durham report, maybe even more importantly — because it's a horrible thing that took place and it should never happen to another president.”

Durham’s inquiry, instigated by Barr, appears to have a broader scope than the inspector general review. Durham’s probe also progressed to a criminal investigation a couple of months ago, officials familiar with the inquiry have said, giving him the power to force testimony from people outside the Justice Department.

Precisely what Durham is investigating criminally remains unclear, but press reports have said that one issue he is examining is whether a then-FBI attorney who handled the Foreign Intelligence Surveillance Act applications for Page, Kevin Clinesmith, altered an email he forwarded related to that work.

The change appears to have downplayed Page’s past help to a U.S. intelligence agency, something that might have undercut suspicions about him.

No charges have been filed over the issue, which was uncovered during the inspector general’s review and referred for possible prosecution. The report says the alteration of the email by the attorney—who is unnamed in the publicly released review—significantly changed the meaning of the email he forwarded, but does not assert it had a material impact on the evidence ultimately sent to the courts.

Horowitz’s review also recommended the FBI consider disciplinary action against various individuals involved in the process.

FBI Director Christopher Wray said he was open to that, but noted that many of those involved have left the bureau.

Wray’s responses to the report seemed to embrace the very finding that Barr rejected: that the launching of the counterintelligence investigation was legitimate.

In an interview Monday, the FBI director was asked whether he thought the bureau had unfairly targeted the Trump campaign.

“I do not,” Wray told ABC News.

A letter Wray issued responding to the report seemed to welcome Horowitz’s conclusion that the Trump-Russia probe was justified, while accepting that the FBI’s handling of surveillance—particularly snooping on U.S. citizens—fell short of the rigorous standards required for such work.

“We are vested with significant authorities, and it is our obligation as public servants to ensure that these authorities are exercised with objectivity and integrity. Anything less falls short of the FBI’s duty to the American people, ” Wray wrote. “Accordingly, the FBI accepts the report’s findings and embraces the need for thoughtful, meaningful remedial action.”

While Clinesmith appears to be the only individual referred for possible prosecution, Sen. Lindsey Graham (R-S.C.), chairman of the Senate Judiciary Committee, said the inspector general’s report made him conclude that multiple people in the FBI process were “liable in a criminal conspiracy.”

“While there may be reasonable differences about whether or not there was a lawful predicate, I believe there will be no debate among reasonable-minded people, particularly lawyers, about how the system not only got off the rails but in my view became the criminal enterprise to defraud the FISA court,” Graham told reporters.

Among the findings in Horowitz’s report is that FBI officials considered and rejected the possibility of informing the Trump campaign about specific individuals of concern with respect to Russian efforts to gain influence over the campaign. Instead, a generic briefing was given about counterintelligence threats, without such details.

Horowitz’s review also found that the FBI used one such briefing as an attempt to gain evidence for its ongoing inquiry into Trump adviser Michael Flynn, who later became national security adviser, was fired and eventually pleaded guilty to a false-statement charge in the Mueller probe.

The inspector general said using such a briefing for investigative purposes was a mistake. Wray agreed and said it would not happen again. “The FBI’s role in these briefings should be for national security purposes and not for investigative purposes,” the FBI chief wrote.

Horowitz is scheduled to appear before the Senate Judiciary Committee on Wednesday to answer lawmakers’ questions about the 20-month-long review.

Horowitz, a former federal prosecutor, was nominated by President Barack Obama in 2011 and confirmed by the Senate to the watchdog job in 2012. The inspector general is not part of the Justice Department chain of command and is supposed to operate independently of the administration.

In advance of Monday’s report, Justice Department observers were keenly watching Barr’s reaction to it and whether he would seek tries to translate, interpret or dispute its findings in a way favorable to Trump.

Barr fueled the narrative about Obama-era dirty tricks against the Trump campaign by opining at a House hearing in April that Trump’s presidential bid had been subjected to “spying” by people in the U.S. government.

“I think spying did occur,” Barr said.

The remark outraged former Justice Department and FBI officials, who faulted Barr for using the provocative term to describe court-approved surveillance begun on a former Trump campaign adviser with less than three weeks to go before the election.

The following month, Barr said he had not meant by his comment to declare that anything improper was done.

“My first job was in CIA and I don't think the word spying has any pejorative connotation, at all. To me, the question is always whether or not it's authorized and adequately predicated,” he told a Senate panel. “I don't consider it a pejorative.”

Natasha Bertrand and Marianne LeVine contributed to this report.