Trump last year abruptly removed Comey who was overseeing a criminal probe into whether the Trump campaign colluded with the Russian government to influence the 2016 presidential election that was won by him.
Comey's explosive book, which is apparently highly critical of Trump, will hit the bookshelves next week.
"Slippery James Comey, a man who always ends up badly and out of whack (he is not smart!), will go down as the WORST FBI Director in history, by far!" Trump said in a tweet.
Refuting the contents of the book, excerpts of which have appeared in the American press, Trump said he never asked Comey for personal loyalty.
"I hardly even knew this guy. Just another of his many lies. His 'memos' are self serving and FAKE!" he said.
"The big questions in Comey's badly reviewed book aren't answered like, how come he gave up Classified Information (jail), why did he lie to Congress (jail), why did the DNC refuse to give Server to the FBI (why didn't they TAKE it), why the phony memos, McCabe's $700,000 & more?" Trump asked.
"Comey throws AG Lynch 'under the bus!' Why can't we all find out what happened on the tarmac in the back of the plane with Wild Bill and Lynch? Was she promised a Supreme Court seat, or AG, in order to lay off Hillary. No golf and grandkids talk (give us all a break)!" tweeted Trump.
Trump recently accused Comey of leaking classified information, saying he should be prosecuted for lying to Congress under oath.
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