He said a salacious allegation that Trump had cavorted with prostitutes in Moscow had left him vulnerable to blackmail by the Russian government. And he asserted that the President was incinerating the country's crucial norms and traditions like a wildfire. He compared Trump to a Mafia boss. "Our President must embody respect and adhere to the values that are at the core of this country," Comey told ABC's chief anchor, George Stephanopoulos, on the program 20/20. Former FBI director James Comey's new book. "The most important being truth. This President is not able to do that. He is morally unfit to be president." The interview with Comey and the publicity tour for his book, which is scheduled to hit bookstores in the US on Tuesday, amount to a remarkable public assault on a sitting president by someone who served at the highest levels in the government.

The stakes for both men could hardly be higher. Comey seems likely to be the star witness in any obstruction of justice case that might be brought against the President by Special Counsel Robert Mueller. Trump's legal fate may depend on whether he succeeds in undermining the credibility of Comey and the law enforcement institutions he views as arrayed against him. While many of Trump's critics believe that the proper remedy for his perceived transgressions is impeachment, Comey insisted that would just "let the American people off the hook". He said the public was "duty bound" to vote Trump out of office in the next election. Loading "You cannot have, as president of the United States, someone who does not reflect the values that I believe Republicans treasure and Democrats treasure and independents treasure," Comey said. "That is the core of this country. That's our foundation. And so impeachment, in a way, would short-circuit that."

Comey's intensely personal attacks - a reflection of his self-righteousness, his detractors say - are all the more combustible because they are aimed directly at a President who has said with pride on Twitter that "when someone attacks me, I always attack back ... except 100x more." As if on cue, hours before the interview aired, Trump called Comey a "slimeball" for the second time in three days, saying in a pair of early-morning Twitter posts that he belonged in jail for what Trump said were lies to Congress and leaks of classified information. In another post, Trump said Comey would go down in history as "the WORST FBI Director in history, by far!" He added that "he is not smart!" Loading Replay Replay video Play video Play video In the ABC interview, Comey had kinder things to say about Trump's brainpower, saying he did not think the President suffered from mental incompetence or was in the early stages of dementia. He said Trump struck him as a person of "above average intelligence". But Comey responded to the President's Twitter posts with a more subtle dig of his own.

"My book is about ethical leadership & draws on stories from my life & lessons I learned from others," he wrote on Twitter. "3 presidents are in my book: 2 help illustrate the values at the heart of ethical leadership; 1 serves as a counterpoint." It is unclear where this epic battle of wills will lead, other than a sustained escalation of insults between two men who have each admitted to having outsize egos. But it is certain to be a test of powerful forces in the modern media landscape: the presidential megaphone, amplified by 50 million Twitter followers, and the global reach of an adversary who is on a seemingly endless, 24-hour, cable-news-driven book tour. The President took a break from his attacks on Comey as he left the White House on a rainy Sunday afternoon, US time, to spend time at Trump National Golf Club in Sterling, Virginia. But it seemed likely that he and his allies would not back down in the face of Comey's barrage of public accusations, which are expected to continue for weeks. New York Times