Donald Trump’s top law enforcement official has dismissed the FBI’s Russia investigation as a “travesty”, rejecting the findings of his own department’s watchdog that cleared it of political bias.

William Barr, the attorney general, claimed the president was the victim of a “bogus narrative” about collusion with Moscow during the 2016 election.

Barr served under Ronald Reagan and George HW Bush but has disappointed observers who hoped he would push back against Trump’s conspiracy theories and blatant lies.

In his first interviews since the justice department’s inspector general said the Russia investigation was justified, Barr told the Wall Street Journal’s CEO Council: “It was a travesty, and there were many abuses. From day one, it generated exculpatory information and nothing that substantiated any kind of collusion.”

In an interview with NBC, Barr said he still had doubts about the FBI’s motives to pursue a “baseless” investigation that stemmed from “flimsy” evidence.

“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,” Barr said, echoing his boss’s criticisms of the media. “I think there were gross abuses … and inexplicable behavior that is intolerable in the FBI.

“I think that leaves open the possibility that there was bad faith.”

Barr pointed out that the FBI used confidential informants who recorded conversations with officials on the Trump campaign. “It was clearly spied upon,” he said. “That’s what electronic surveillance is … going through people’s emails, wiring people up.”

The report by the justice department’s inspector general was released on Monday. It said there was no political bias in the origin and operation of the FBI’s investigation of Russian election interference and links between Trump and Moscow – a common charge by the president and his allies who allege a supposed “deep state” conspiracy.

But the inspector general, Michael Horowitz, did find “serious performance failures” in the monitoring of Carter Page, a Trump aide linked with Moscow. Horowitz found 17 “significant inaccuracies or omissions” in applications for a warrant from the Foreign Intelligence Surveillance or Fisa court to monitor Page’s communications and subsequent renewals.

The attorney general said he disagreed with Horowitz’s conclusion that the FBI had enough information to surveil Page. Officials withheld from judges what he said was key exculpatory information, Barr added.

The attorney general’s broadside put him at odds with Democrats, intelligence community figures and the current head of the FBI, Christopher Wray.

On ABC on Monday, Wray was asked if he believed the FBI unfairly targeted the Trump campaign.

“I do not,” he said. “I think it’s important that the inspector general found that, in this particular instance, the investigation was opened with appropriate predication and authorisation.”

Trump lashed out. “I don’t know what report current director of the FBI Christopher Wray was reading,” he tweeted, , “but it sure wasn’t the one given to me. With that kind of attitude, he will never be able to fix the FBI, which is badly broken despite having some of the greatest men & women working there!”

Trump had apparently been watching Fox News, one side of reliably partisan media responses to the report.

“You have to look at the 17 instances of misconduct cited in the Report,” Trump wrote, “they are very bad. The Fisa court was clearly taken for a ride on this, a failure of the FBI up and fown [sic] the chain of command. It’s about as strong a medicine as I’ve seen in a report of this kind in a very long time.”

Wray also pushed back on the conspiracy theory that Ukraine intervened in the 2016 election, a line followed by Trump and his supporters.

He told ABC: “We have no information that indicates that Ukraine interfered with the 2016 presidential election.”

The president has fired an FBI director before – James Comey, in May 2017, perhaps the most consequential act of his presidency prior to the impeachment inquiry.

On Tuesday, Trump also took aim at familiar characters: “The FBI has had some dark day in its past, but nothing like this. This was VERY SERIOUS MISCONDUCT ON THE PART OF THE FBI. … Are you listening Comey, McCabe, lovers Lisa & Peter, the beautiful Ohr family, Brennan, Clapper & many more?”

Andrew McCabe is a former deputy director of the FBI, fired by Trump. Bruce and Nellier Ohr are a justice department official and his wife, who worked with the political intelligence company Fusion GPS. John Brennan was director of the CIA under Barack Obama, and James Clapper was director of national intelligence.

The “lovers Lisa & Peter” are Lisa Page, a former FBI lawyer, and Peter Strzok, a former FBI agent. Strzok was fired in the fallout from the Comey firing..

Page claimed vindication. She tweeted on Monday: “The sum total of findings by IG Horowitz that my personal opinions had any bearing on the course of either the Clinton or Russia investigations? Zero and Zero.”

Comey was similarly satisfied, writing in the Washington Post that Horowitz demonstrated “the allegation of a criminal conspiracy was nonsense. There was no illegal wiretapping, there were no informants inserted into the campaign, there was no ‘spying’ on the Trump campaign. Although it took two years, the truth is finally out.”

But Christopher Steele, an ex-British intelligence operative, disputed some of the inspector general’s assertions. His lawyers claimed the report “contains several serious errors and misstatements”, including the portrayal of Steele as a confidential human source (CHS).

“Christopher Steele repeatedly told the FBI that he could not be a CHS because his obligations to his former government employer prohibited his acting in such a capacity,” the statement said.

Steele also denied that the FBI asked him not to speak to the media and criticised the report for appearing to suggest his intelligence agency, Orbis, was inaccurate in its reporting on Page.