Former FBI Director James Comey is sworn in prior to testifying before a Senate Intelligence Committee hearing on Russia's alleged interference in the 2016 U.S. presidential election on Capitol Hill in Washington, U.S., June 8, 2017. REUTERS/Jonathan Ernst - HP1ED681D7GSU

James Comey, who was fired from the FBI in May 2017, wrote in a soon-to-be-released memoir that Trump was like a mob boss who is "untethered to the truth."  (Reuters/Jonathan Ernst)

What's in James Comey's book? 5 revelations from the fired FBI director's memoir

Former FBI Director James Comey has an explosive book coming out this week – and several leaked passages have already made headlines.

In his book, titled “A Higher Loyalty: Truth, Lies and Leadership,” Comey, 57, compared Trump to a mob boss who is “untethered to the truth.” The ousted FBI director also said Trump’s presidency has been “ego driven and about personal loyalty.”

The president and his aides have lambasted Comey, who was fired in May 2017, ahead of the book release.

“He is a weak and untruthful slime ball who was, as time has proven, a terrible Director of the FBI,” Trump said of Comey. “It was my great honor to fire James Comey!”

But as he's promoted his memoir, Comey has continued to take shots at the president, calling him "medically" and "morally" unable to be president. 

Here’s a look at five passages from the upcoming memoir.

'Loyalty dinner'

A copy of former FBI director James Comey's book "A Higher Loyalty" is seen in New York City, New York, U.S. April 13, 2018.  REUTERS/Soren Larson - RC131B5D4890

A copy of former FBI director James Comey's book "A Higher Loyalty."  (Reuters/Soren Larson)

As reported by Axios, Comey discussed what’s become known as the “loyalty dinner” he had with Trump at the White House in January 2017, right after the inauguration. Comey had previously testified before a Senate panel that Trump asked him if he wanted to keep his job during the dinner.

“He said lots of people wanted to be director of the FBI, but that he thought very highly of me,” Comey wrote, according to Axios. “He said he had heard great things about me and knew the people of the FBI thought very highly of me as well.”

“He said despite that, he would understand if I wanted to ‘walk away’ given all I had been through, although then he noted that that would be bad for me personally because it would look like I had done something wrong,” Comey continued.

Comey described the dinner as “strange” because he said Trump had “decided my job security was on the menu.”

Trump said, “I need loyalty. I expect loyalty,” at the meeting, ABC News reported.

“Now it was pretty clear to me what was happening. The setup of the dinner, both the physical layout of the private meal and Trump’s pretense that he had not already asked me to stay on multiple occasions, convinced me this was an effort to establish a patronage relationship,” Comey said.

Comey compared Trump’s quest for loyalty to “Sammy the Bull’s Cosa Nostra induction ceremony” in the book, according to ABC. Salvatore Gravano – or “Sammy the Bull” – is a former mobster who helped the FBI put the late gangster John Gotti in prison.

‘Investigate the prostitute claim for Melania’

Trump considered having Comey launch an investigation into the claims about his interactions with Russian prostitutes in the now-infamous dossier, the former FBI director wrote in the memoir, according to the New York Post.

The salacious but unverified dossier compiled by ex-British spy Christopher Steele alleged that Trump asked Russian prostitutes to urinate on a Moscow hotel bed in a room that former President Barack Obama and first lady Michelle Obama had stayed in before.

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Comey wrote that Trump “brought up what he called the ‘golden showers things’ … adding that it bothered him if there was ‘even a 1 percent chance’ his wife, Melania, thought it was true.”

“He just rolled on, unprompted, explaining why it couldn’t possibly be true, ending by saying he was thinking of asking me to investigate the allegation to prove it was a lie,” Comey wrote, according to the New York Post. “I said it was up to him.”

Comey said he warned Trump if he did investigate the claim, it could “create a narrative that we were investigating him personally.” He said Trump told him the allegation couldn’t be true because he’s a “germaphobe.”

Comey then speculated about the state of Trump’s marriage if the first lady would even think there’s a 1 percent chance the claim in the dossier was true.

“In what kind of marriage, to what kind of man, does a spouse conclude there is only a 99 percent chance her husband didn’t do that?” Comey said in his book.

A Loretta Lynch mystery

Attorney General Loretta E. Lynch stands during the announcement of law enforcement action against the state of North Carolina in Washington, U.S., May 9, 2016.      REUTERS/Joshua Roberts/File Photo - TM3EC6K14FB01

In his memoir, James Comey hinted at a secret involving former Attorney Gen. Loretta Lynch.  (Reuters/Joshua Roberts)

Comey hinted about a secret involving former Attorney Gen. Loretta Lynch that – should it come out – would “undoubtedly have been used by political opponents to cast serious doubt on the attorney general’s independence in connection with the Clinton investigation.”

Lynch fueled speculation that she was biased in favor of Democratic presidential nominee Hillary Clinton – even during the investigation into her use of a private email server during her tenure as secretary of state – when she infamously met with former President Bill Clinton on her plane on a Phoenix airport tarmac in July 2016. The oft-speculated about meeting occurred just days before Comey said he would not recommend charges against Clinton, despite calling her handling of classified information “extremely careless.”

According to ABC News, Comey said in his memoir that he took on more of a role with the email investigation because of something involving Lynch that was a “development still unknown to the American public to this day.”

He said the information about Lynch, according to ABC News, came from a still-classified source.

“Had it become public, the unverified material would undoubtedly have been used by political opponents to cast serious doubt on the attorney general’s independence in connection with the Clinton investigation,” he said.

Rep. Trey Gowdy, R-S.C., told Fox News there were “a lot of things that called into question the legitimacy” of the Clinton email investigation.

“It wasn’t the tarmac, it was the information he had about Loretta Lynch that if it became public, people would question their objectivity,” Gowdy said.

Obama’s blessing

Even throughout the controversy surrounding the FBI’s handling of the Clinton email investigation, Obama still gave Comey praise, he wrote in his book.

“I picked you to be FBI director because of your integrity and your ability. I want you to know that nothing has happened in the last year to change my view,” Obama told him, according to Business Insider.

Comey said Obama’s encouragement nearly made him cry.

“Boy, were those words I needed to hear … I’m just trying to do the right thing,” Comey said.

Obama responded by saying, “I know.”

The Washington Post reported that, "Perhaps the only politician who comes off well in the excerpts so far is Obama."

John Kelly’s offer

After he was fired, Comey wrote that John Kelly, then the secretary of Homeland Security, offered to quit his job in protest in an “emotional call,” The New York Times reported. Kelly is now Trump’s chief of staff.

Comey said Kelly told him he was “sick” about his ousting. According to the Daily Beast, Kelly told Comey he “didn’t want to work for dishonorable people.”

“I urged Kelly not to do that, arguing that the country needed principled people around this president,” Comey wrote of Kelly’s offer. “Especially this president.”

Fox News’ Adam Shaw and The Associated Press contributed to this report.

Kaitlyn Schallhorn is a Reporter for Fox News. Follow her on Twitter @K_Schallhorn.