Donald Trump’s son-in-law and senior White House adviser, Jared Kushner, tried to persuade the publisher of the Washington Post to fire its editor over coverage of the Russia investigation, that editor, Marty Baron, writes in a new book.

“With no delay and without pause during his four years as president,” Baron writes, “Trump and his team would go after the Post and everyone else in the media who didn’t bend to his wishes.

“In December 2019, Kushner would lean on [Fred] Ryan to withdraw support for me and our Russia investigation.

“… ‘He aims to get me fired,’ I told Ryan.”

Baron’s book, Collision of Power: Trump, Bezos and the Washington Post, will be published next Tuesday. The Guardian obtained a copy.

The book arrives amid renewed attacks on the press by Trump. Last week, the former president turned Republican frontrunner promised action against Comcast, owner of MSNBC and NBC, for “country-threatening treason”.

The Post won a Pulitzer prize (shared with the New York Times) for its coverage of the investigation of Russian election interference in 2016 and links between Trump and Moscow.

At the end of that investigation, in spring 2019, the special counsel, former FBI director Robert Mueller, did not indict Trump or say he colluded with Russia. But Mueller did lay out extensive evidence of potential obstruction of justice by Trump and secure multiple indictments and convictions of Trump aides and allies.

Trump claimed exoneration – which Mueller did not offer – and called for prizes awarded for Russia reporting to be rescinded; calls rejected by the Pulitzer board.

Kushner, Baron now writes, “suggested the Post issue an apology and there be a ‘reckoning of some sort’ – as he advised that he himself had made a huge mistake in once standing by a former editor of the New York Observer and one of its stories when he owned the publication.

“‘Standing by my editor at that time was my biggest regret in the 10 years I owned the newspaper,’ he wrote in the email to Ryan. Kushner’s intent was clear to me. ‘He aims to get me fired,’ I told Ryan.”

The Post did not apologise. Baron was not fired. He retired in 2021, after a stellar career that included a Boston Globe investigation of sexual abuse in the Catholic church that won a Pulitzer and became an Oscar-winning movie, Spotlight, in which Baron was played by Liev Schreiber.

The first excerpt of Collision of Power was published by the Atlantic. Though Baron says his book is “not strictly a memoir”, the excerpt described a “confidential” dinner Trump held for the Post owner, Jeff Bezos of Amazon, Baron, Ryan and another editor, Fred Hiatt, early in his presidency.

It was the night of the Congressional Baseball Game, 15 June 2017, which Trump chose not to attend despite the shooting during practice of Steve Scalise of Louisiana, a House Republican leader and Trump supporter, who was then fighting for his life.

Trump chose to address the game by video and to dine with journalists instead.

Though the decision was put down to “security reasons”, Baron writes, “the president’s image could not have been enhanced if, at such a fraught moment, the public knew he chose to spend his time with the very sorts of media people whom he called the ‘lowest form of life’.

“Away from the memorial, Trump would pass the evening with us crowing about his election victory, mocking his rivals and even some in his own orbit, boasting already of imagined accomplishments, calculating how he could win yet again in four years, and describing the Washington Post as the worst of all media outlets.”

“As we dined on cheese soufflé, pan-roasted Dover sole, and chocolate cream tart, he went on to disparage other media outlets – the New York Times came in just behind us in his ranking at the time, whose journalists he had labeled for months as scum and garbage.”

Baron describes further boorish behavior by Trump, including repeatedly jabbing Baron’s shoulder with his left elbow.

Kushner, he says, was also “bristling at the attention, both from investigators and the press. He had called and emailed my boss, Ryan, fretting over what headlines might say and labeling as ‘jackasses’ the national security reporters digging into his Russia contacts. He followed up with a series of agitated emails, even copying in Bezos (‘Looping in Jamie [Gorelick, his lawyer] who can vouch on this with Jeff since she knows him well,’ read one), while declining to speak directly to the reporters involved and steadfastly avoiding communication directly with me.

“In a meeting later that week with White House correspondents Philip Rucker and Ashley Parker as well as national editor Steven Ginsberg, he pounded a table in fury, wailing about the good life he and Ivanka had left behind in New York and the potential injury to his reputation. As the Post journalists made their exit, Kushner patted Steven on the back, declaring, ‘Well, that was therapeutic.’”

The morning after the White House dinner, Baron says, Kushner “called Ryan … to get his read on how the dinner went.

“After Fred offered thanks for the generosity and graciousness with their time, Kushner inquired whether the Post’s coverage would now improve as a result. Ryan diplomatically rebuffed him with a reminder that there were to be no expectations about coverage.”

Calls between Kushner and Ryan have been reported elsewhere, not least by Kushner in his own memoir, Breaking History.

Since Trump left the White House, Kushner and his wife, Trump’s daughter Ivanka, have assumed relative distance. But Trump has not left the scene.

Despite facing 91 criminal charges – for election subversion, retention of classified information and hush money payments – and civil threats including investigations of his business affairs and defamation arising from an allegation of rape, Trump leads Republican polling by huge margins.