Five months before the 2020 election, Bill Barr fired Geoffrey Berman, the US attorney for the southern district of New York.

Trying to justify the decision, Barr twisted himself into a pretzel. Donald Trump had not nominated Berman. Jeff Sessions, Barr’s predecessor as attorney general, named him to the post on an interim basis and a panel of federal judges kept him on. Barr’s authority to rid himself of this troublesome prosecutor was at best disputable.

Revenge is best served cold. Two years and three months later, Berman is back with a memoir, Holding the Line. In the annals of Trump alumni revenge porn, it is an instant classic. It is smart and crisp. It is full of bile and easy to read.

Barr wrote his own book. He has toured the TV studios, seeking rehabilitation. Over 350 pages, Berman immolates all that.

He also tells the public what Trump and his own transition team knew from the outset: Rudy Giuliani was “unhinged”, and friends with the bottle. The chaos of Giuliani’s work as Trump’s attorney, through impeachment and insurrection, cannot have been a surprise. It may be surprising, though, that he was once in contention to be secretary of state.

Berman also pulverizes Trump’s contention that Merrick Garland’s justice department is hyper-politicized. Berman shows that under Trump, Main Justice was a haven for lackeys all too willing to do the big guy’s bidding. He accuses Trump of weaponizing the justice department, pushing it to prosecute his critics and enemies while sparing his friends.

After New York prosecutors brought charges against Michael Cohen, Trump’s one-time fixer, and Chris Collins, a New York congressman, the powers-that-be purportedly advised Berman: “It’s time for you guys to even things out.”

Practically, that meant launching an investigation at Trump’s behest into John Kerry, for allegedly violating the Logan Act in talks with Iranian officials after retiring as secretary of state.

Briefly, the Logan Act, from 1798, bars non-government officials from negotiating with foreign powers. In the case of Greg Craig, Barack Obama’s White House counsel, it meant charges under the Foreign Agents Registration Act. After Berman unsuccessfully argued that Craig should not have been prosecuted, Craig was acquitted by a federal jury. Kerry was never indicted.

Berman is a Republican. He volunteered on Trump’s 2016 campaign and was once a law partner of Giuliani. He is also a former editor of the Stanford Law Review, happy to punch up. As with most Trump memoirs, Holding the Line is full of score-settling. Berman calls Barr a liar, a bully and a thug.

Writing about his dismissal, Berman says: “I would describe Barr’s posture that morning as thuggish. He wanted to bludgeon me into submission.”

“If you do not resign from your position, you will be fired,” Barr purportedly warned. “That will not be good for your resume and future job prospects.”

Think of Berman as the honey badger – if the honey badger headed up a white-collar practice at a Wall Street law firm. He doesn’t give a fig. He holds the receipts.

“Several hours after Barr and I met,” he writes, “on a Friday night, [Barr] issued a press release saying that I was stepping down. That was a lie.”

“A lie told by the nation’s top law enforcement officer.”

Barr’s stints in government are emblematic of the descent of the Republican party in the last 30 years. Barr was George HW Bush’s attorney general. Next time round he was simply Trump’s guy at Main Justice.

Barr coddled Mike Flynn, Paul Manafort and Roger Stone. He marched to St John’s church with the president and misled the public about the use of teargas to disperse protesters. More than once, his relationship with the truth drew the ire of the federal bench. His last-moment departure from the Trump administration bore all the marks of the arsonist who flees when the flames grow uncomfortably close.

As for Giuliani, Berman portrays him as a boozy and incoherent Islamophobe. In the spring of 2016, Berman organised a “cross-selling dinner” to introduce Giuliani and other lawyers to clients “at a large financial institution”. Things headed south. Giuliani “continued to drink”. The dinner morphed into “an utter and complete train wreck”.

At one point, Berman writes, Giuliani turned to a man “wearing a yarmulke [who] had ordered a kosher meal”. Under the impression the man was a Muslim, Giuliani said: “I’m sorry to have tell you this, but the founder of your religion is a murderer.”

“It was unbelievable,” Berman gasps. “Rudy was unhinged. A pall fell over the room.”

Two years later, the law firm, Greenberg Traurig, shoved Giuliani out the door. He had opined that hush-money payments made via a lawyer were perfectly normal, even when not authorised by the client. In the case in question, Michael Cohen acted as a conduit between Stormy Daniels, an adult film star, and Trump.

“That was money that was paid by his lawyer, the way I would do, out of his law firm funds,” Giuliani told Fox News. “Michael would take care of things like this, like I take care of this with my clients.”

Cohen pleaded guilty to federal charges – and became a target of Trump’s animus and Barr’s vengeance.

These days, Giuliani is in the cross-hairs of prosecutors in Fulton county, Georgia, over Trump’s attempt to overturn his defeat in the state. Trump’s own legal exposure appears to grow almost hourly. Barr surmises that an indictment may be imminent.

From the looks of things, Geoffrey Berman is having the last laugh.

• Holding the Line: Inside the Nation’s Preeminent US Attorney’s Office and Its Battle with the Trump Justice Department is published in the US by Penguin Press