Originally Published: 27 JUN 21 15:23 ET

Updated: 28 JUN 21 08:01 ET

By Devan Cole, CNN

(CNN) -- Former Attorney General William Barr, in a newly released book excerpt, said he suspected then-President Donald Trump's claims of widespread election fraud were "all bullsh*t," but that he launched unofficial inquiries into some of them to appease his boss.

The comments from Barr -- published in The Atlantic as part of an excerpt from "Betrayal," a book set to publish in November focusing on the final days of the Trump administration from ABC News chief Washington correspondent Jonathan Karl -- provide insight into the Trump loyalist's mindset in the waning days of the administration, when he delivered the most credible blow to Trump's unfounded claims that the 2020 election was littered with fraud during an interview with the Associated Press.

"But Barr told me he had already concluded that it was highly unlikely that evidence existed that would tip the scales in the election. He had expected Trump to lose and therefore was not surprised by the outcome. He also knew that at some point, Trump was going to confront him about the allegations, and he wanted to be able to say that he had looked into them and that they were unfounded," the excerpt from Karl reads.

"So, in addition to giving prosecutors approval to open investigations into clear and credible allegations of substantial fraud, Barr began his own, unofficial inquiry into the major claims that the president and his allies were making."

Barr told Karl that his "'attitude was: It was put-up or shut-up time,'" adding: "'If there was evidence of fraud, I had no motive to suppress it. But my suspicion all the way along was that there was nothing there. It was all bullsh*t.'"

While Barr resigned from his post nearly two weeks after telling the Associated Press that the Justice Department had not found any such evidence of fraud, his split with Trump was mostly -- at least publicly -- amicable, with the former official using his resignation letter to offer a glowing account of Trump's tenure.

Karl, however, writes in his book that after Barr's interview with the AP, he and Trump traded barbs during a tense meeting at the White House in which the former President pressed his attorney general on why he publicly rejected the election claims.

"'How the fk could you do this to me? Why did you say it?'" Trump asked Barr, to which he replied: "'Because it's true.'"

"The president, livid, responded by referring to himself in the third person: 'You must hate Trump. You must hate Trump,'" the excerpt reads.

For his part, Barr took aim at the legal strategy Trump was efforting at the time with the help his personal attorney Rudy Giuliani, telling the president that any election-related legal challenges "would have taken a crackerjack team with a really coherent and disciplined strategy."

"Instead, you have a clown show. No self-respecting lawyer is going anywhere near it. It's just a joke. That's why you are where you are," Barr said, according to the excerpt.