An FBI investigation into the Donald Trump election campaign’s alleged collusion with Russia was justified and not motivated by political bias against him, a government watchdog has concluded.

A report by the justice department’s inspector general demolished three years of claims by the president that he was the victim of a “deep state” conspiracy and that the investigation was based on a dossier compiled by an ex-British intelligence operative, Christopher Steele.

“The report issued today by the inspector general debunks the conspiracy theories about the Mueller report and the Russia investigation that President Trump and Republicans in Congress have pushed for years,” Jerrold Nadler, the chair of the House judiciary committee, and Carolyn Maloney, the chair of the House oversight committee, said in a joint statement.

“Those discredited conspiracy theories were attempts to deflect from the president’s serious and ongoing misconduct, first urging Russia and now extorting Ukraine into interfering with our elections to benefit himself personally and politically.”

But the report by the inspector general, Michael Horowitz, did pinpoint “serious performance failures” in the monitoring of a Trump aide, which the president’s allies seized on in an attempt to claim vindication.

Horowitz identified 17 “significant inaccuracies or omissions” in applications for a warrant from the Foreign Intelligence Surveillance or Fisa court to monitor the communications of the former Trump adviser Carter Page and subsequent warrant renewals.

The errors resulted in “applications that made it appear that the information supporting probable cause was stronger than was actually the case”, the report said, although the FBI had a legal “authorized purpose” to ask for court approval.

The attorney general, William Barr, rejected Horowitz’s conclusion that there was sufficient evidence to open the investigation.

“The inspector general’s report now makes clear that the FBI launched an intrusive investigation of a US presidential campaign on the thinnest of suspicions that, in my view, were insufficient to justify the steps taken,” Barr said.

However, the inspector general concluded there was no evidence to support the claim by Trump and his supporters that he would uncover bias in the top ranks of the FBI.

The president has repeatedly suggested the Russia investigation was driven by Barack Obama’s justice department because it wanted Hillary Clinton to win the White House.

Andrew McCabe, the former deputy director of the FBI, has been demonised by Trump. McCabe’s counsel, Michael Bromwich, said “the review found an ample factual basis for the launching of the Russia investigation. It also found unanimity – among FBI and DoJ personnel at every level – that the investigation needed to be opened, and that not doing so would have been a dereliction of duty by the FBI.”

The investigation, ultimately taken over by the special counsel Robert Mueller, started in July 2016 after the FBI learned that George Papadopoulos, a former Trump aide, had been saying before it was publicly known that Russia possessed dirt on Clinton in the form of hacked emails.

It was this, not the so-called “Steele dossier”, that was the trigger. Horowitz found that the FBI had overstated the significance of Steele’s past work as an informant and left out information about one of Steele’s sources whom Steele called a “boaster” who “may engage in some embellishment”.

The report also says law enforcement officials failed to offer “greater clarity on the political origins and connections” of Steele’s reporting, including the fact that the political research firm that selected him had been hired by Democrats.

Intriguingly, Horowitz made reference to Steele having met a member of the Trump family at Trump Tower in 2010. According to ABC News, which viewed communications between them, the family member was Trump’s daughter, Ivanka, who wanted to discuss the possibility of Steele working for the Trump Organization on overseas business.

The report states: “Steele called the allegation that he was biased against Trump from the start ‘ridiculous’. He stated that if anything he was ‘favourably disposed’ toward the Trump family before he began his research because he had visited a Trump family member at Trump Tower and ‘been friendly’ with [the family member] for some years.

“He described their relationship as ‘personal’ and said he once gifted a family tartan from Scotland to the family member.”

The report says the FBI also sent an informant to record a conversation with a “high-level Trump campaign official” who was not considered a subject in the Russia investigation. The official was not named.

This is not the end of the saga. A separate criminal investigation continues, overseen by Barr and led by a US attorney, John Durham.

Extraordinarily, Durham weighed in on Monday, issuing a statement that said “we do not agree with some of the report’s conclusions as to predication and how the FBI case was opened”.

Matthew Miller, the chief spokesman at the justice department under Obama, responded on Twitter: “Why is he commenting on the incomplete findings of an ongoing investigation he is conducting? This is totally inappropriate and a sign of real rot setting in at DoJ. Shut up until you’re finished.”

The inspector general report comes as Trump faces an impeachment inquiry in Congress centered on his efforts to have Ukraine investigate a political rival, Joe Biden.

Trump ignored the report’s conclusions and reiterated a baseless claim of victimhood.

“It’s a disgrace what’s happened with respect to the things that were done to our country,” he said at the White House. “It should never again happen to another president. It is incredible, far worse than I ever thought possible, and it’s an embarrassment to our country, it’s dishonest.”



In instant response to the president’s remarks, Frank Figliuzzi, a former FBI assistant director, told the MSNBC network: “We are officially living in an alternate reality. I have the IG report in my hand. I can assure you the president hasn’t read it and is lying about it.”



Meanwhile, the FBI director, Christopher Wray, welcomed the “constructive criticism” offered by the report and said he had offered more than 40 “corrective steps” to address its recommendations. This includes modifying processes under the Foreign Intelligence Surveillance Act, both for initial applications and renewals.