"Virtually everyone in Washington thought he should be fired for the terrible job he did-until he was, in fact, fired," the US president wrote on Twitter. "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.
"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. It was my great honor to fire James Comey!"
Mr Comey's book, A Higher Loyalty, which is set to go on sale next week, provides a detailed account of his interactions with Mr Trump, who he says appears to be "untethered to truth" and "ego driven".
He casts Mr Trump as a mobster-like figure who sought to blur the line between law enforcement and politics and tried to pressure him personally regarding his investigation into Russian election interference.
The book adheres closely to Mr Comey's public testimony and written statements about his contacts with Mr Trump, and his growing concern about the billionaire's integrity.
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