Former FBI director James Comey says that US President Donald Trump is a dangerous, morally unfit leader doing tremendous damage to institutional norms.
Comey, fired by Trump in May last year, was worried the president may be open to blackmail by Russia.
Comey's firing came as the Federal Bureau of Investigation was probing possible connections between Trump's 2016 presidential campaign and Russia's meddling in the American elections.
Russia has denied interfering in the election and Trump has denied any collusion or improper activity.
Comey said in the interview with ABC News' George Stephanopoulos, which aired on Sunday night that it is "possible, but I don't know" whether Russia has evidence to back up the allegations about Trump's Moscow trip.
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"A person ... who talks about and treats women like they're pieces of meat, who lies constantly about matters big and small and insists the American people believe it, that person's not fit to be president of the United States, on moral grounds. And that's not a policy statement," Comey said.
"He is morally unfit to be president," he added.
Comey has a tell-all book, "Higher Loyalty," due out on Tuesday.
The book's imminent release - and the slated ABC News interview - prompted Trump to hurl a new set of insults at Comey earlier on Sunday, challenging accusations made in the book, and insisting that he never pressed Comey to be loyal to him.
"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 wrote early on Sunday in one of five Twitter posts aimed directly at Comey.
In the book, Comey wrote that Trump, in a private meeting, pressed the then-FBI director for his loyalty.
Comey said the title of the book came from a "bizarre conversation" he had with Trump at the White House in January 2017 shortly after his inauguration.
"He asked for my loyalty personally as the FBI director. My loyalty's supposed to be to the American people and to the institution," Comey said.
The FBI has long tried to operate as an independent law enforcement agency.
"I 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!" Trump said on Twitter.
