Donald Trump’s second attorney general, William Barr, is stupid, a liar, a bully and a thug, according to a hard-hitting new book by Geoffrey Berman, the US attorney for the southern district of New York whose firing Barr engineered in hugely controversial fashion in summer 2020.

“Several hours after Barr and I met,” Berman 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.”

Trump’s politicisation of the US Department of Justice was a hot-button issue throughout his presidency. It remains so as he claims persecution under Barr’s successor, Merrick Garland, regarding the mishandling of classified information, the Capitol attack and multiple other investigations.

Berman describes his own ordeal, as Barr sought a more politically pliant occupant of the hugely powerful New York post, in Holding the Line: Inside the Nation’s Preeminent US Attorney’s Office and its Battle with the Trump Justice Department, a memoir to be published next week. The Guardian obtained a copy.

Berman testified in Congress shortly after his dismissal. He now writes: “No one from SDNY with knowledge of [his clashes with Barr over two and a half years] has been interviewed or written about them. Until now, there has not been a firsthand account.”

Berman describes clashes on issues including the prosecution of Michael Cohen, Trump’s former fixer, and the Halkbank investigation, concerning Turkish bankers and government officials helping Tehran circumvent the Iran nuclear deal.

Barr was also attorney general under George HW Bush. He has published his own book, One Damn Thing After Another: Memoirs of an Attorney General, in which he discusses SDNY affairs but does not mention Berman. Promoting the book, Barr told NBC he “didn’t really think that much about” his former adversary.

Berman calls that “an easily disprovable lie”.

In Berman’s book, Barr is a constant presence. Describing the Halkbank case, Berman says Trump’s closeness to Recep Tayyip Erdoğan, the Turkish president, meant Barr was, “always eager to please his boss, appeared to be doing Trump’s bidding” by leaning on Berman to drop charges.

Berman says Barr told him he, Barr, would be “point person” for the administration on Halkbank, which Berman found “odd”.

“This is a criminal case being run out of New York, right? As attorney general, Barr had a role to play. But why as White House-designated point person? That was problematic.”

Berman says Barr tried to block the SDNY to benefit Trump politically. In June 2019, he says, he was summoned to a meeting where Barr told him the Halkbank case “implicates foreign policy” and, “his voice … steadily rising”, asked: “Who do you think you are to interfere?”

He writes: “I’ve seen bullies work before. In fact he had used the same words with me a little more than a year before” over the appointment of Berman’s deputy, Audrey Strauss, without Barr’s approval.

Berman adds: “I would describe Barr’s posture that morning as thuggish. He wanted to bludgeon me into submission.”

Berman turned Barr down. He also says he told Barr a proposal to offer individuals in the Halkbank case a non-prosecution agreement without disclosing the move would be “a fraud on the court”.

The Halkbank issue eventually dropped away, after Trump and Erdoğan fell out over the US withdrawal from Syria. But Barr and Berman’s enmity remained.

Berman also gives his version of events in June 2020, when Barr summoned him to a meeting at the Pierre hotel in New York City.

Berman first delivers a sharp aside about Barr’s ostentatious travel, his apparent ambitions – Berman speculates that the attorney general wanted to be secretary of state in Trump’s second term – and an infamous, secretive meeting between Barr and Rupert Murdoch that Berman calls “a scene right out of HBO’s Succession”.

Berman says he did not know why Barr wanted to meet him, but thought it might be because he had refused to sign a letter attacking Bill de Blasio, then mayor of New York, over the application of Covid restrictions to religious services and protests for racial justice. Berman did not sign, he writes, because he could not be seen to act politically.

At the Pierre, he says, Barr, who with his chief of staff was not wearing a mask indoors, said he wanted to “make a change in the southern district”. Berman says he knew what would come next, given changes elsewhere to instal Barr allies and moves to influence investigations of Trump aides including Roger Stone and Michael Flynn.

“The reason Barr wanted me to resign immediately was so I could be replaced with an outsider he trusted,” Berman writes, adding that he was not sure he could be removed other than by the judges who appointed him to fill the office on an interim basis in 2018, or by Senate confirmation of a successor.

Berman turned down Barr’s offer. He says Barr then made an “especially tawdry” suggestion: that if Berman moved to run the DoJ civil division, “I could leverage it to make more money after I left government”. Berman says Barr also asked if he had civil litigation experience, a question Berman deems “almost comical”. Then Barr threatened to fire him.

Berman “thought to myself, what a gross and colossal bully this guy is to threaten my livelihood”. He did not budge. Barr said he would think of other jobs. After the meeting, Berman writes, Barr asked if he would like to lead the Securities and Exchange Commission. Berman says that job “was not [Barr’s] to offer”, as the SEC chair is nominated by the president and Senate confirmed.

Berman says he agreed to talk to Barr again after the weekend. Instead, that night Barr issued a press release saying Berman had agreed to resign.

“It was a lie, plain and simple,” Berman writes. “I clearly told him I was not stepping down. Barr [was] the attorney general … in addition to being honest, he should be smart. And this was really stupid on his part – a complete miscalculation … he should have known at this point that I was not going to go quietly.”

In a press release of his own, Berman said he had not resigned. The next day he showed up for work, greeted by a swarm of reporters. Then, in a public letter Berman now calls “an idiotic diatribe”, Barr said Berman had been fired by Trump.

Barr did drop a plan to replace Berman with an acting US attorney, instead allowing Berman’s deputy, Strauss, to succeed him. Berman says that enabled him to step aside in good conscience. He calls Barr’s move a “surrender”.

Berman describes both his belief he was fired because his independence represented “a threat to Trump’s re-election” and Trump’s insistence to reporters on the day of the firing that he had not fired Berman – Barr had.

“Barr’s attempt to push me out,” he writes, “was so bungled that he and Trump couldn’t even get their stories straight.”