A former top federal prosecutor in New York alleges in his new book that his office repeatedly faced pressure from the Justice Department under ex-President Donald Trump to pursue politically motivated cases.

“Throughout my tenure as U.S. attorney, Trump’s Justice Department kept demanding that I use my office to aid them politically, and I kept declining — in ways just tactful enough to keep me from being fired,” Geoffrey Berman writes in “Holding the Line: Inside the Nation's Preeminent US Attorney's Office and Its Battle with the Trump Justice Department,” according to The New York Times.

“I walked this tightrope for two and a half years,” Berman adds. “Eventually, the rope snapped.”

Berman was fired as U.S. attorney for the Southern District of New York in June 2020 after his office took a number of actions that frustrated Trump, including the prosecution of Michael Cohen and an investigation into Rudy Giuliani, both of whom served as Trump’s private attorneys.

In an interview with ABC’s “Good Morning America” on Monday, Berman said the pressure his office faced extended beyond those cases.

“I had never seen anything like that before. … People who had been in the office for 40 years never saw anything like that,” he said. “It was unprecedented and scary.”

Berman’s allegations come as Trump and his allies argue without evidence that the Biden administration is using the Justice Department and FBI as political weapons by having them investigate Trump for holding hundreds of government documents — many mark classified — at his home after leaving office.

Berman writes that in May 2018, just after Trump posted a pair of tweets alleging former Secretary of State John Kerry, a Democrat, engaged in potentially illegal conversations with Iranian officials about the Iran nuclear deal, the Justice Department told the Southern District it would be responsible for a related investigation into Kerry that would be accompanied by the FBI.

“Two tweets by the president and the John Kerry criminal case becomes a priority for the Department of Justice,” Berman, who worked on Trump’s 2016 campaign and transition team, told ABC News. “And the statute they wanted us to use was enacted in 1799 and had never been successfully prosecuted.”

The statute, the Logan Act, bars private citizens from unauthorized negotiations with foreign governments. 

Berman wrote that Kerry never learned of the investigation. 

The former federal prosecutor also alleges that in September 2018 Edward O’Callaghan, then the principal associate deputy attorney general, contacted Berman’s office pointing to the prosecutions of Cohen and U.S. Rep. Chris Collins, R-N.Y., a Trump ally, and asking to “even things out” by charging, before the midterm elections, Gregory Craig, a White House counsel under President Barack Obama. Craig was being accused of failing to register as a foreign agent for work he had done years earlier for the Ukrainian government and for lying to the Justice Department.

The Southern District investigated the case months earlier. Berman said he believed Craig did not violate the Foreign Agents Registration Act and did not file charges, the former prosecutor writes in his book, which will be released Tuesday.

The U.S. attorney in Washington agreed to take the case. Craig was indicted for making false statements, but a jury acquitted him after deliberating for five hours.

“It was vindication, but the case should never have been brought,” Berman told ABC. “I was on the phone with the U.S. attorney from the District of Columbia trying to convince her not to indict Greg Craig. The case was too weak to be brought. It was inappropriate to be brought. And that's what the trial showed.”

O’Callaghan told The Times that Berman’s characterization of his actions in the case are “categorically false.”

Berman also says the Justice Department asked his office to remove references to “Individual 1” in documents when Cohen pleaded guilty in 2019 to nine charges related to paying hush money to porn actress Stormy Daniels and Playboy model Karen McDougal, whom Trump allegedly had affairs with. “Individual 1” referred to Trump.

“They were unsuccessful in that venture, and they were unsuccessful in every attempt to politically interfere with our office,” Berman told ABC News.

Trump’s office did not immediately respond to a request for comment Monday morning.