Lawyers who have filled political appointee positions in the Trump administration have been pursued by doubts about their qualifications or caliber.

In 2018, a justice department staffer was made acting attorney general, the department’s top job.

Last week, the president installed a young friend of his aide Stephen Miller atop a pyramid of 2,500 lawyers as general counsel in the Department of Homeland Security.

But there is one Trump appointee whose preparedness has never been questioned. William Barr, 69 and a veteran of 40 years in Washington, was confirmed one year ago as attorney general, a position with broad influence over the administration of justice and broad sway over public faith placed in it.

“Barr is particularly effective,” said Paul Rosenzweig, a senior fellow at the R Street Institute and veteran of the George W Bush administration, “because he’s one of the very few exceptions among Trump appointees – someone who is both qualified to do the job and has sufficient experience to know how to do it well.

“Sadly, he has decided to be an enabler.”

At the end of a historically turbulent week for the justice department with unknown implications for the country, that combination in Barr – power plus a knack for wielding it – has provoked intense alarm in Washington and far beyond.

The fear is that Barr’s competence has flipped from virtue to vice owing to a quality that he appears to lack or have lost: judgment in the face of an untethered president.

Trump’s actions reflect his belief that he really has, as he said, an absolute right to intervene anywhere Paul Rosenzweig

Barr was once seen as a potential check on Trump’s overt desire to take command of the justice department, deploying its investigators and prosecutors at his whim and his will. But this week, critics warn, the attorney general has been revealed as an eager accomplice in eroding norms meant to insulate the criminal justice system from political interference, threatening the bedrock principle of equality before the law.

“We fought a revolution against kingly prerogative,” said Rosenzweig. “At its most extreme, Trump’s actions post-impeachment in the last week reflect his belief that he really has, as he said, an absolute right to intervene anywhere in the executive branch. And there’s a word for that.

“People with absolute rights are kings.”

Trump has never been coy about his intentions. On Friday morning, he fed the sense of alarm when he insisted that he has “the legal right” to intervene in criminal cases.

Donald Trump and William Barr: in lockstep? Photograph: The Washington Post via Getty Images

But the developments of the past week have changed the public understanding of just how aligned Barr is with the president, and just how extensive his cooperation has been.

Those developments included Barr’s intervention in a case involving Trump’s friend Roger Stone, prompting the withdrawal of four career prosecutors; the resignation from government of a prominent former US attorney previously sidelined by Barr; and the issuance of a rare public warning by a federal judge about the independence of the courts.

“Bill Barr has turned the job of attorney general and the political appointee layer at the top of the justice department on its head,” said Neil Kinkopf, a Georgia State law professor who worked in the Office of Legal Counsel under Bill Clinton.

“In past administrations of both political parties, the function of the political appointees at the justice department has been to insulate the rest of the department from political pressure. And Bill Barr instead has become the conduit for that political pressure.”

‘Shrewd, careful and full of it’

Barr has not been untouched by the turbulence of the last week. Reported threats of additional resignations drove him on Thursday to grant a TV interview in which he complained that Trump’s tweets “make it impossible for me to do my job” and vowed: “I’m not going to be bullied or influenced by anybody.”

A Trump spokesperson said the president’s feelings were not hurt. Barr was said to have warned the White House of what he was going to say.

The interview was met with outrage and eye-rolls among critics who saw a wide divergence between what Barr said and everything else he has been doing.

“I think Bill Barr is shrewd, deliberate, smart, calculating, careful, and full of it,” tweeted the former US attorney Preet Bharara.

The real Barr, critics say, has a 12-month track record as a spearhead for Trump’s attack on justice, beginning with public lies about the report of special counsel Robert Mueller and running through his intervention in the case of Roger Stone.

A cardboard cutout of William Barr is seen as protesters hold signs which read “Barr Coverup,” following the release of the Mueller report on 18 April 2019. Photograph: Carlos Barría/Reuters

In a prominent early incident among many in which Barr’s loyalty to the president seemed to critics to exceed his loyalty to the nation, Barr called a press conference last April and offered a misleading preview of Mueller’s report. He omitted the report’s detailed description of potential obstruction of justice by Trump and falsely claimed the White House had cooperated fully.

In May, Barr assigned a US attorney to investigate the origins of the Russia investigation, an obsession of Trump’s. In July, Barr traveled to London to ask intelligence officials there for help with the investigation. He made a similar trip to Italy in September.

Recently, Barr announced the creation of an “intake process” for information gathered by Rudy Giuliani about investigations tied to Joe Biden and Hillary Clinton. On Friday, the New York Times reported that Barr had assigned outside prosecutors to review the prosecution of the former national security adviser Michael Flynn and other defendants tied personally to Trump.

In August, Barr declined to recuse himself from a justice department review of a whistleblower complaint charging Trump with soliciting foreign interference in the 2020 election, despite his being named in the report. The review found no wrongdoing by the president, who survived impeachment over the matter.

This kind of direct, presidential interference in specific ongoing criminal prosecutions is extraordinary Neil Kinkopf

But no previous action by Barr provoked such a crisis as his intervention this week in the Stone case.

In that episode, Barr directed the US attorney’s office in the District of Columbia, which handles many prominent cases with a nexus to the federal government, to revisit its recommendation of seven to nine years in prison for Stone, who was convicted of obstruction of justice and witness tampering among other felonies.

It was unclear whether Barr issued his direction before or after a Trump tweet blasting the case as “a horrible and very unfair situation” and a “miscarriage of justice”. In any event, the US attorney, a hand-picked Barr ally, entered a new recommendation for a lighter sentence and the four career prosecutors who signed the original recommendation withdrew from the case in apparent protest.

“I do think it is something of a break-the-glass moment because of how overt it is,” said Harry Sandick, a former assistant US attorney in the southern district of New York who helped draft a letter published by the New York City bar association on Wednesday calling for an “immediate investigation”.

Kinkopf said: “This is a really significant break. This kind of direct, presidential interference in specific ongoing criminal prosecutions is extraordinary. Even for this president and this attorney general.”

Barr’s intervention in the Stone case came after he orchestrated a replacement of the head of the prosecutor’s office in Washington, Jessie Liu, under murky circumstances. Liu had been tapped for a Treasury post and was replaced in the US attorney’s office by Timothy Shea, a Barr loyalist. Then, this week, Trump withdrew Liu’s nomination – and she resigned from government.

Barr’s intervention in the Roger Stone case was described as a ‘break-the-glass’ moment by one former US attorney. Photograph: Andrew Harrer/Bloomberg via Getty Images

“One wonders whether other tweets could lead to people being charged, to people seeking harsher sentences,” said Sandick. “We watch with concern over the possibility that the US attorney in Washington DC was replaced because of her unwillingness perhaps to charge [former FBI official] Andrew McCabe, or James Comey, or others.”

A further Trump attack this week on the judge in the Paul Manafort and Stone cases, as well as the DC prosecutors, prompted a rare rebuke on Thursday from the chief US judge in the District of Columbia, Beryl A Howell.

“The judges of this court base their sentencing decisions on careful consideration of the actual record in the case before them; the applicable sentencing guidelines and statutory factors; the submissions of the parties, the Probation Office and victims; and their own judgment and experience,” Howell said.

“Public criticism or pressure is not a factor.”

‘Immense suffering, wreckage and misery’

Barr grew up in New York City, graduated from George Washington University law school, served in the Reagan administration and was attorney general under George HW Bush, establishing a record as a hardliner on gang violence and immigration and advocating for pardons in the Iran-Contra affair.

He is a devout Catholic, describing in a speech in October at the University of Notre Dame how the American experiment depends on the advance of “Judeo-Christian moral standards” and attacking “militant secularists” whose “campaign to destroy the traditional moral order has brought with it immense suffering, wreckage and misery”.

Barr’s long career in public life led some justice department veterans to welcome his nomination as attorney general in late 2018, given concerns about who else Trump might pick.

There was some hope that he would be an attorney general in the traditional model … he has been a grave disappointment Paul Rosenzweig

“Initially there was some hope that he would be an attorney general in the traditional model,” said Rosenzweig. “And I confess that myself, I thought that would be the case and I thought it would be a pretty traditional appointment.

“And he has been a grave disappointment.”

But there were also warnings about Barr, particularly attached to a memo he submitted to the department arguing that Mueller’s investigation of Trump for alleged obstruction of justice was “fatally misconceived”.

Kinkopf was among those who warned that Barr’s view of executive power was dangerously expansive, telling the Guardian it “comes very close to putting the president above the law”.

But there was room to believe at the time that Barr’s theories would remain theories, Kinkopf says now.

“Even among people who have advocated that theory of presidential power,” he said, “there are very longstanding norms in the justice department and the White House about respecting the independence of the justice department.”

Barr has not vindicated his supporters, Kinkopf said.

“His theory is that the constitution allows for this, but good-faith service in the office of president and the office of attorney general maintains the credibility and the apolitical nature of law enforcement. That had long been the norm regardless of one’s view of presidential power.

“Barr has completely obliterated that.”