President Donald Trump on Friday morning attacked James Comey on Twitter.

Details of the former FBI director's new book began to emerge this week.

In the book, set to be released Tuesday, Comey is said to be highly critical of Trump, comparing the president to a mob boss.

President Donald Trump took aim at James Comey in a Friday-morning Twitter tirade after unflattering details emerged from the former FBI director's new book.

"James Comey is a proven LEAKER & LIAR. Virtually everyone in Washington thought he should be fired for the terrible job he did-until he was, in fact, fired," Trump tweeted. "He leaked CLASSIFIED information, for which he should be prosecuted. He lied to Congress under OATH. He is a weak and untruthful slime ball who was, as time has proven, a terrible Director of the FBI."

Over the past several days, excerpts of Comey's new book, "A Higher Loyalty," and teasers from a coming ABC interview have revealed the former FBI director's highly critical opinion of the president. Comey is said to have compared Trump to a mob boss, criticized Trump's physical appearance, and detailed the president's focus on the salacious accusations contained in the dossier compiled by the former British spy Christopher Steele.

Comey also reportedly recounted meetings with Trump in which he has already publicly said Trump asked for his loyalty and requested that Comey end the FBI investigation into Michael Flynn, Trump's first national security adviser. Those meetings are now a focus of the special counsel Robert Mueller's investigation.

Trump fired Comey in May 2017, ostensibly for the FBI director's handling of the Hillary Clinton email scandal, which the president also mentioned Friday during his Twitter attacks.

"His handling of the Crooked Hillary Clinton case, and the events surrounding it, will go down as one of the worst 'botch jobs' of history," Trump said. "It was my great honor to fire James Comey!"

Comey's book also recounts John Kelly's reaction to Comey's firing. Kelly, Trump's chief of staff who was then the secretary of homeland security, was "sick" after hearing the news and "intended to quit" in protest, Comey reportedly said in the book.

The Trump administration and Republicans have joined Trump in attempting to discredit Comey's claims. The Republican National Committee launched a campaign against Comey that includes a website, Lyincomey.com, and TV ads.

Kellyanne Conway, a counselor to the president, also blasted Comey during a Fox News interview on Friday.

"He sounds like a disgruntled ex-employee who after the fact wants to clear his conscience of what bothered him at the time," Conway said. "If you're that bothered, quit, leave the job."