Practically everybody knows the dossier is a collection of lies, except Comey, who seems to know very little - save for the alleged size of Trump's hands.
The attacks come hours before Comey's interview with ABC's George Stephanopoulos was scheduled to air Sunday night.
In a subsequent exchange, Ryan reiterated his view that special counsel Robert S. Mueller III ought to be left to complete his investigation into the Trump orbit.
Trump reacted on Twitter early Friday, the day after the emergence of details from Comey's memoir, which says Trump is "untethered to truth", and describes him as fixated in the early days of his presidency on having the Federal Bureau of Investigation debunk salacious rumors he said were untrue but that could distress his wife.
Refuting the contents of the book, excerpts of which have appeared in the American press, Trump said he never asked Comey for personal loyalty. "It was smaller than mine, but did not seem unusually so", Comey reportedly wrote in his book, describing the moment he first met the president previous year. Comey told ABC News that after this, Trump said something that distracted him: "He said, 'If there's even a one percent chance my wife thinks that's true, that's awful'".
White House spokeswoman Sarah Huckabee Sanders said on Twitter Friday: "One of the few areas of true bipartisan consensus in Washington is Comey has no credibility". In a Monmouth University poll last May, the numbers were almost identical with 10% of Democrats approving of Trump's to fire Comey compared with 74% of Republicans.
Comey finally broke the silence on the salacious allegations from a dossier which stated that Russian authorities recorded US President Donald Trump watching prostitutes urinate in a hotel suite in Moscow in 2013.
"No one, to my recollection, asked so what's coming next from the Russians, how might we stop it, what's the future look like", Comey said.
In that initial meeting, Comey wrote, the Trump team determined that they would emphasize that the Russians had no impact on the 2016 presidential election.
"James Comey is a proven LEAKER & LIAR", Trump said.
He leaked CLASSIFIED information, for which he should be prosecuted.
"James Comey, a man of integrity?" She also took issue with some of Comey's personal commentary in the book, saying it was "no way to comport oneself after you're trying to prove that you have this quote, 'higher loyalty'".