After years of shrugging his shoulders at the Russian attack on the 2016 election, Donald Trump has accelerated an inquiry into the US intelligence agencies whose investigation of the Russian plot ultimately focused on his presidential campaign.

The president gave the attorney general, William Barr, the unilateral authority to declassify intelligence documents and ordered the US intelligence community to “quickly and fully cooperate” with Barr’s work, in an official memorandum issued late on Thursday.

Former intelligence officials warned that the move represented a dangerous enlargement of Barr’s authority and that it could undermine ongoing investigations of ongoing hostile activity by Russia.

It’s “very unusual – unprecedented in my experience – for a non-intelligence officer to be given absolute declassification authority over the intelligence,” David Kris, former head of the justice department’s national security division, told the Associated Press.

“Make no mistake,” tweeted Asha Rangappa, a former FBI special agent and Yale faculty member. “If Barr discloses the identities of CIA and [counter-intelligence] sources providing information on Russia he is disabling our intelligence capacities *to Russia’s advantage*. It puts sources providing intelligence in danger and cripples the [intelligence community’s] ability to recruit new sources.”

Max Boot, a columnist and fellow at the Council on Foreign Relations, quipped: “So Trump’s position is that his tax returns should be kept private but the CIA’s ‘sources and methods’ should be made public.”

Trump has accused former FBI officials of “treason” and calls the investigation of his campaign, which had hundreds of secret contacts with Russian operatives as Moscow attacked the US election, a “witch-hunt”. Special counsel Robert Mueller said in a report issued earlier this spring that an investigation had uncovered no evidence of any Trump campaign member knowingly entering into the Russian conspiracy.

Trump’s ire at Mueller has in recent weeks produced a multi-pronged “investigation of the investigators” led by Barr, who appointed a US attorney to investigate the FBI counterintelligence investigation and who has called surveillance of the Trump campaign conducted with a court-issued warrant “spying”.

Carrie Cordero, a senior fellow at the Center for New American Security, wrote on the Lawfare blog that the attorney general and president should not be throwing around words like “spying” and “treason” to describe the counterintelligence investigation.

“There are serious reasons to conduct a review of policies and procedures governing national security investigations involving political campaigns,” Cordero wrote. “But the administration’s rhetoric diminishes the legitimate value that this review could bring.”

Jim Baker, the former FBI counsel, has said that the investigation of the Trump campaign began after the former Trump aide George Papadopoulos allegedly bragged to an Australian diplomat during a night of drinking in July 2016 about the campaign having damaging information on Hillary Clinton. The diplomat went to the FBI.

“That was the nugget of information that got everything going,” Baker said, adding: “It would have been a dereliction of our duty not to investigate this information, again, given the fact that we’d been focused on the Russians as threat actors for a long time, given what was going on with respect to email dumps and hacking.”

John Sipher, a former CIA employee, urged the intelligence leadership to defend the rank-and-file against Trump’s onslaught.

“If this is a legitimate effort to learn about the trustworthiness of the intel,” Sipher tweeted, “Easy, There are established processes. If it is an effort to find scapegoats to help with partisan deflection (like Trump did with FBI), then leadership needs to fall on its sword and refuse to play.”

Walter Shaub, a former director of the Office of Government Ethics and a senior adviser to Citizens for Responsibility and Ethics in Washington (Crew), told the Guardian last week that the appropriate way for the justice department to interrogate any concerns about the Russia investigation was through the inspector general’s office.

“I think it’s extremely troubling that Barr has now assigned a handpicked investigator to look into the investigation run by his own agency,” Shaub said. “They have an inspector general for a reason, and the inspector general for the Department of Justice is one of the most respected inspectors general that there is, or ever has been. There’s no reason not to rely on him if you’re looking for the truth.”

The White House said in a statement accompanying Trump’s memo that Barr is looking for the truth: “Today’s action will ensure that all Americans learn the truth about the events that occurred, and the actions that were taken, during the last presidential election and will restore confidence in our public institutions.”