WASHINGTON — The Justice Department’s inspector general on Wednesday painted a bleak portrait of the F.B.I. as a dysfunctional agency that severely mishandled its surveillance powers in the Russia investigation, but told lawmakers he had no evidence that the mistakes were intentional or undertaken out of political bias rather than “gross incompetence and negligence.”
While Democrats emphasized that the inspector general, Michael E. Horowitz, had debunked President Trump’s accusations that the F.B.I. conspired to overthrow his presidency, Mr. Horowitz insisted that his report was no exoneration, citing the serious errors, omissions and misleading statements he found in court wiretap filings.
“It doesn’t vindicate anybody at the F.B.I. who touched this, including the leadership,” Mr. Horowitz told members of the Senate Judiciary Committee.
While Democrats and Republicans clung to their political talking points, lawmakers on both sides also agreed that the surveillance problems Mr. Horowitz uncovered were severe. Several suggested that Congress should amend the Foreign Intelligence Surveillance Act, or FISA, to tighten permissions for national-security wiretapping.
Since it was released on Monday, Mr. Horowitz’s report has largely been interpreted through a political lens. Because it debunked Mr. Trump’s conspiracy theories and concluded that investigators had a legitimate and lawful basis to open the inquiry, some — like the F.B.I. director at the time, James B. Comey — have portrayed it as vindication.
But Senator Lindsey Graham of South Carolina, the Republican chairman of the committee, argued that the most important finding was instead the portrayal of a systemic and cultural failure of accountability at the F.B.I. that permitted grievous mistakes to make their way into filings seeking court permission to wiretap a former Trump campaign adviser, Carter Page.
Mr. Graham opened the hearing by acknowledging that the government of Russia — not Ukraine — sought to interfere with the 2016 election, and he did not quarrel with Mr. Horowitz’s finding that the F.B.I. had a legitimate basis to open a full counterintelligence investigation into links between Russia and people associated with the Trump campaign.
But he portrayed the wiretapping of Mr. Page as dubious and said it should have stopped after January 2017, when the F.B.I. had reason to lose confidence in evidence it used to obtain the initial court order targeting him. Mr. Horowitz’s findings about the wiretap applications should disturb all Americans, no matter their political leanings or the motivations behind the F.B.I. officials’ actions, he said.
“My goal is to make sure that people, when this is over — whether you like Trump, hate Trump, don’t care about Trump — you look at this as more than a few irregularities,” Mr. Graham said. “If this becomes a few irregularities in America, then God help us all.”
The bureau first obtained court permission to wiretap Mr. Page in October 2016, and obtained three extensions of that order in 2017. Mr. Horowitz’s report found lapses in all four filings.
In some cases, F.B.I. officials working on the investigation, called Crossfire Hurricane, selectively cited evidence, telling the Justice Department information that made Mr. Page look suspicious and omitting materials that cut the other way. The department passed that misleading portrait onto the court.
For example, the filings omitted that Mr. Page had told the C.I.A. about some of his meetings with Russians through the years, disclosures that made those encounters look less suspicious. Mr. Horowitz found that an F.B.I. lawyer misled a colleague as they prepared a wiretap renewal application, altering an email in a way that prevented the court from learning about Mr. Page’s dealings with the C.I.A.
And in January 2017, the F.B.I. interviewed a source for Christopher Steele, the British former intelligence agent who compiled a dossier of unverified claims about Mr. Trump and Russia that was used to win the warrant. The interview raised serious doubts about Mr. Steele’s material, but the bureau left that out of its renewal applications, telling the court only that it had found the source to be cooperative and credible — creating a misleading impression.
“There is no planet on which I think this report indicates that things were O.K. within the F.B.I.,” said Senator Mike Lee, Republican of Utah.
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Republicans also argued that the failings should be viewed through the lens of text messages in which F.B.I. officials expressed political opposition to Mr. Trump, challenging Mr. Horowitz’s conclusion that he had found no documentary or testimonial evidence of an anti-Trump plot at the bureau.
“It looks like they were trying to skate along the edges and get away with something,” said Senator Thom Tillis, Republican of North Carolina, who derisively labeled the investigators the “Misfire Hurricane” team.
“I can’t imagine they did it than any other reason than a political motivation,” he added.
Mr. Horowitz emphasized that while he found no evidence that the errors and omissions in the surveillance materials were intentional, he also said he was unsatisfied with the explanations for the mistakes — such as that officials were busy with other investigative tasks. He noted that he could not read people’s minds to learn their motivations.
Some liberal lawmakers who have long sought to impose tighter controls on government surveillance powers welcomed conservative interest in enacting such legislation. Among them was Senator Richard Blumenthal, Democrat of Connecticut, who noted that he introduced an unsuccessful bill to tighten FISA rules in 2013.
“I hope that we can make use of your expertise in this area and I hope my Republican colleagues who have been so vocal and vehement about the dangers of potential FISA abuses will join me in looking forward and reform of that court,” he told the inspector general.
Mr. Horowitz also clarified why a prosecutor conducting his own review of the Russia investigation had disputed findings in his report.
The F.B.I. opened the investigation as a “full” counterintelligence inquiry, and John H. Durham, the United States attorney investigating the Russia inquiry at the behest of Attorney General William P. Barr, believed it should have been a “preliminary” one, Mr. Horowitz said.
Mr. Durham had mentioned the disagreement in a highly unusual statement after Mr. Horowitz’s report was released but had not detailed it. Mr. Horowitz said that he stood by his conclusion and that neither Mr. Durham nor Mr. Barr has presented any information that changed his mind.
Mr. Durham did say that the F.B.I. had sufficient information “to support the preliminary investigation,” Mr. Horowitz said.
Under F.B.I. standards, agents can open a preliminary investigation on “any allegation or information” that indicates possible criminal activity or threats to national security. Opening a full investigation requires “an articulable factual basis” that “reasonably indicates” that a crime or security threat exists.
The F.B.I.’s head of counterintelligence at the time, Bill Priestap, opened the Russia investigation in 2016 after WikiLeaks began publishing stolen Democratic emails believed to have been hacked by Russia, and after the bureau learned that a Trump campaign aide suggested that the Russians wanted to coordinate the release of information that could damage Hillary Clinton’s campaign.
Republican senators also expressed alarm at the hearing that an F.B.I. agent collected information about Mr. Trump and Michael T. Flynn, a top adviser at the time, while briefing them on counterintelligence risks to the Trump campaign in August 2016.
The agent thought the briefing would be a good opportunity to make himself familiar with Mr. Flynn, who was one of the four Trump associates under investigation and might need to be questioned later. In the days afterward, the F.B.I. agent wrote a memo based on his observations of Mr. Trump and Mr. Flynn and added it to the Russia investigation file. (Mr. Flynn eventually pleaded guilty to lying months later to the same F.B.I. agent about his conversations with the Russian ambassador to the United States at the time.)
The episode highlighted a key complaint by Trump allies about the Russia inquiry: that investigators improperly intruded on the campaign. Though Mr. Horowitz did not uncover any instances of agents flouting policy in the investigative steps they took, critics have called for the F.B.I. to reconsider its lack of restrictions on opening investigations that involve scrutiny of constitutionally protected activities, such as political campaigns.
Asked whether the move was typical, Mr. Horowitz said there was no policy forbidding it, then mentioned that the F.B.I. director, Christopher A. Wray, had insisted that it would “not happen going forward.
“I think it’s pretty clear what his state of mind is on that: This should not have occurred,” Mr. Horowitz said.