In his 22 months as attorney general under Donald Trump, Bill Barr played blocking back and spear-catcher for the 45th president.

Only when Trump tried to steal the election did Barr grow a conscience. Otherwise, he was a close approximation to Roy Cohn, Trump’s notorious and long-dead personal attorney. Cohn and Barr even attended the same high school and college. But in the end, much as Trump ditched Cohn as he lay dying of Aids, Trump discarded Barr.

Elie Honig surmises that Barr’s quest for power and desire to turn the clock back on secular modernity girded his disdain for democratic norms and legal conventions that came to stand in his way.

Honig is an ex-prosecutor who became a CNN commentator. His first book, subtitled “How Bill Barr Broke the Prosecutor’s Code and Corrupted the Justice Department”, catalogs Barr’s misdeeds across 288 pages, interspersed with flashbacks to Honig’s career as an assistant US attorney in the southern district of New York.

Honig successfully prosecuted more than 100 members and associates of organized crime, including bosses and members of the Gambino and Genovese families. More recently, he drew a comparison between such “mafia cases” and Trump’s Goodfellas-tinged lexicon.

“Calling somebody who provides information to law enforcement a ‘rat’ is straight up mob boss language,” Honig tweeted in late 2018.

Suffice to say, the author’s anger toward Barr is real and Hatchet Man is thorough. Barr’s transgressions are laid out in black and white.

In March 2019, less than two months after succeeding Jeff Sessions, Barr released his own preview of Robert Mueller’s report on Russian election interference and links between Trump and Moscow – a preview notably untethered to fact. Later, Barr put his fingers on the scale in connection with the sentencing of Roger Stone and the early release of Paul Manafort. For a self-professed law-and-order AG, who also served under George HW Bush but who had never prosecuted a criminal case, these were unusual steps, to say the least.

The federal bench came to question Barr’s credibility. In an opinion tied to the release of a memo related to Barr’s summary of the Mueller report, US district judge Amy Berman Jackson wrote that both Barr and the Department of Justice had been “disingenuous”.

The Biden administration is appealing against the ruling. Preserving presidential authority takes precedence over the public’s right to know. Buffing DoJ’s halo can be left for another day.

Another of Barr’s gambits, seeking to toss Michael Flynn’s guilty plea (for lying to the FBI while national security adviser) before he received a pardon, became a lightning rod. US district judge Emmett Sullivan questioned Barr’s legal gymnastics.

“In view of the government’s previous argument in this case that Mr Flynn’s false statements were ‘absolutely material’ because his false statements ‘went to the heart’ of the FBI’s investigation, the government’s about-face, without explanation, raises concerns about the regularity of its decision-making process,” Sullivan observed.

Yet as Trump-era books go, Hatchet Man fails to sizzle. It is short on news and does not entertain. Those with first-hand knowledge did not share it with Honig. Rather, his book is a lament and a prayer for an idealized version of Main Justice that seldom ever was.

The power to prosecute and defend is a potent weapon and politics weighs in the balance. John F Kennedy tapped Bobby Kennedy, his brother, as attorney general. Richard Nixon placed John Mitchell, his law partner, in the job. Alberto Gonzales, George W Bush’s counsel since his days as Texas governor, held on until he was forced out. His tenure was a hot mess. The usual question for attorneys general is not whether they are “political” but rather “how political” they are.

Under Barack Obama, Loretta Lynch declined to recuse herself from the investigation of Hillary Clinton’s email use while attempting to steer James Comey from the shadows where he tried to do his work. The FBI director criticized Lynch’s attempt to recast the investigation as a “matter”.

Seeing the hand of the Clinton campaign in this kerfuffle over semantics, Comey wrote that the FBI “didn’t do ‘matters’” and “it was misleading to suggest otherwise”.

At the other end of the spectrum stands Edward Levi, attorney general under Gerald Ford. Appointed to clear the Augean stables after the Nixon years, Levi was a rarity. A University of Chicago professor, he named an independent counsel to investigate a mere rumor that Ford had received illegal contributions from maritime unions. A six-month investigation found no wrongdoing – and may have torpedoed Ford’s bid for a full term in power.

Honig lauds Lynch’s trial experience. Levi’s grandson, Will Levi, was Barr’s chief of staff. It’s a small world, after all.

An entire chapter of Hatchet Man, meanwhile, is devoted to Barr’s decision to inject the government into a defamation lawsuit brought against Trump by the writer E Jean Carroll.

In 2019, Carroll wrote that Trump sexually assaulted her more than two decades before. Trump said she was “totally lying” and that he knew “nothing about her”.

After Carroll requested a DNA sample, Barr removed the lawsuit to federal court and claimed Trump’s comments were made within the scope of his official duties. Honig calls the government’s arguments “specious”. A federal trial judge agreed.

Not surprisingly, the Trump administration appealed. More surprisingly, Merrick Garland, Biden’s attorney general, has declined to drop that appeal. In the words of one commentator: “There’s nothing new about the justice department protecting the executive branch and the president.”

Honig writes that the DoJ “must enact new, on-the-books policies out of the ditch” Barr dug, in an attempt to restore post-Watergate norms. Call that wishful thinking. What ails the department is what ails America: division and political warfare. Another piece of legislation or a well-crafted executive order is not about to change that.

• Hatchet Man is published in the US by Harper