Attorney general William Barr’s controversial decision to launch a new inquiry into the origins of the FBI’s 2016 Russia investigation has fueled concerns about the politicization of the justice department and could hamper attempts to combat Kremlin meddling in the 2020 election, say ex-top DoJ and CIA officials, and key Democrats.

Critics say that Barr’s investigation – which partially overlaps another one by the DoJ’s own inspector general – will probably be used by Donald Trump’s re-election campaign to fuel attacks on the special counsel Robert Mueller’s critical conclusions about Russian interference in the 2016 election and subsequent obstruction efforts by the president.

Some critics see it as an overtly political “investigation into the investigators” that is pandering to Trump’s oft-repeated claims that his 2016 election campaign was targeted by the so-called “deep state” in an effort to thwart his election.

Barr’s review will scrutinize the FBI and key intelligence agencies involved in the initial stages of the 2016 Russia investigation which the FBI launched as a counter-intelligence investigation to examine early signs of Russian meddling in the election.

John Sipher, who served in the CIA’s National Clandestine Services for 28 years with a stint leading its Russia operations, said: “Trump with Barr’s help is trying to craft a narrative of a coup aimed at his campaign.” Sipher added: “The attorney general has shown a willingness to play ball with Trump. Barr has been willing to back up Trump.”

Sipher said Barr’s review was “hunting for scapegoats”.

Among the key figures Trump and allies have often attacked for their roles in the Russia investigation which they vilify as a “witch-hunt” are: former FBI director James Comey, ex-CIA director John Brennan, ex-FBI agent Peter Strzok and ex-FBI lawyer Lisa Page. Some Trump aides and allies have called on these figures to be prosecuted.

“Even if nothing is found they’ve spun up their [political] base. There’s no downside,” Sipher said.

Mary McCord, a former top DoJ prosecutor who led the department’s national security division until spring 2017, said that launching a review into the genesis of the Russia investigation meant Barr was “allowing the president to have an open issue going into the 2020 elections that allows the whole witch-hunt” mantra to gain traction.

Trump’s delight with Barr’s sweeping non-criminal review, led by the US attorney for Connecticut, John Durham, has been palpable. “I am so proud of our attorney general that he is looking into it,” Trump has said. “I think it’s great.”

Trump’s faith in Barr was also underscored when he gave him oversight of the review, passing over the director of national intelligence, Dan Coats, who would normally oversee such an investigation, the former FBI general counsel Jim Baker said. Coats has previously bumped heads with Trump over several national security issues.

“It’s a slap in the face to Coats,” said Baker, who worked closely in the initial stages of the Russia investigation with Comey. “A legitimate question is: ‘Why is the AG doing this as opposed to Coats?’

“It’s clear that the president has confidence in Barr,” added Baker, who now leads the national security and cyber security program at R Street Institute, a nonpartisan public policy group. Baker noted that Trump issued an unusual and controversial executive order that gives Barr broad authority to declassify intelligence documents and make them public as part of the review.

A DoJ spokesperson declined to answer several questions about the Barr-Durham review, including its expected duration. Durham’s office also declined comment.

In a 10 June letter to the Democratic chair of the House judiciary committee, a top DoJ official described the new review as “broad in scope and multifaceted”. The DoJ letter said the goal was to “more fully understand the efficacy and propriety” of the FBI’s 2016 counterintelligence inquiry into Russian meddling. The FBI, the CIA and the DNI were instructed by Trump to cooperate – which all are doing.

Mark Warner, the top Democrat on the Senate intelligence committee, said in a a statement he was worried Barr’s inquiry could impede counterintelligence efforts to thwart more Kremlin interference, which the FBI expects again in the 2020 election.

Warner said Barr’s review could have a “chilling effect on future counterintelligence investigations”.

I’m deeply concerned that the president and the attorney general seem determined to weaponize and politicize intelligence that people risk their lives to obtain Mark Warner

Warner expressed worry that Trump and Barr were using their powers over national security and intelligence issues for political purposes. “I’m deeply concerned that the president and the attorney general seem determined to weaponize and politicize intelligence that people risk their lives to obtain,” Warner said.

Some DoJ veterans say concerns about Barr’s decision to launch his new review are misplaced, noting his deep legal background in government, including a stint as attorney general under George HW Bush .

“There is no way to know now what Barr will find in his investigation or whether or how he will use this power,” Jack Goldsmith, a conservative ex-DoJ official and now a Harvard Law School professor, told the New York Times. “But Barr is not someone inclined to harm our national security bureaucracy.”

Before Trump tapped Barr in late 2018 to replace the former attorney general Jeff Sessions, whom Trump often attacked for recusing himself from overseeing the Mueller investigation due to conflicts, Barr was well known as a champion of robust executive powers, a stance that probably made him attractive to Trump.

Concerns about Barr were compounded when he sparked a separate political firestorm by issuing a misleading and short four-page summary of Mueller’s report, and then taking a few weeks to release a redacted version of the 448-page document.

Mueller’s report provided granular details about how the Trump campaign welcomed the Kremlin’s multifaceted cyber and social media disinformation operation in 2016 to help Trump, including hacking of Democratic computers by Russian agents and ads by fake groups on Facebook.

The report also cited more than 100 meetings and contacts between Trump campaign aides and Russians. Kremlin interference, which initially focused on sowing confusion among voters but shifted to helping Trump defeat Hillary Clinton, was “sweeping and systematic”, Mueller concluded.

Mueller’s report also documented 10 instances of possible Trump obstruction, but concluded that he lacked the power to charge the president due to justice department guidelines, while stressing that the report did not exonerate Trump.

Just days later, Barr announced that since Mueller did not reach a conclusion, he felt it necessary to do so and, with help from the then deputy attorney general, Rod Rosenstein, concluded there were insufficient grounds for charging Trump with obstruction.

As Barr was launching his investigation, he raised eyebrows in congressional testimony by saying he had “concerns” there might have been “spying” on Trump campaign members, as the president had often charged.

But when pressed, Barr said he had no evidence to support Trump’s allegations.

Barr is “playing to conspiracy theorists by using the term spying”, said Sipher. “Trump and Barr are using language to confuse people rather than clarify.”

Other Barr testimony has raised fears he is taking political cues from Trump. At one Senate committee early last month, Barr was asked several times by Democratic senator Kamala Harris if Trump or anyone in the White House had suggested or pressured him to launch his broad review. Barr was evasive, but acknowledged there had been some “discussions” of the matter, adding that “they have not asked me to open an investigation”.

Ron Wyden, a top Democrat on the Senate intelligence panel, is troubled by the direction that Barr’s review seems to be taking and the powers Trump has handed him.

“Trump has been searching for years for someone to selectively declassify intelligence and throw dirt on the Russia investigation,” Wyden said in a statement. Trump, he added, “wants any shred of misleading evidence that will validate his self-serving conspiracy theories. William Barr has embraced that role.”

Likewise, Sipher stressed that the powers Trump granted Barr to declassify intelligence seem part of a political game. “By suggesting you need to declassify materials, you’re suggesting there’s been criminality or improper behavior, [and] pushing the narrative of a deep state conspiracy,” Sipher said.

That’s wrong, said Baker, saying that the FBI launched its investigation to deal with a genuine national security threat from Russia, as detailed in the Mueller report.

“Mueller’s conclusions validated our initial investigation, which was focused on Russia,” Baker said, adding that Mueller’s detailed report about Russia’s multi-pronged interference in 2016, makes it impossible to “conclude anything but this was a legitimate investigation”.