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"A person who sees moral equivalence in Charlottesville, 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," Comey said, citing last year’s white nationalist rally in Charlottesville, Virginia.
Comey's critique aired Sunday in an interview with ABC News chief anchor George Stephanopoulos before the Tuesday release of his new book, "A Higher Loyalty: Truth, Lies, and Leadership."
Comey, 57, dismissed the speculation about Trump's mental capabilities that he said "I often hear people talk about."
"I don't buy this stuff about him being mentally incompetent or early stages of dementia. He strikes me as a person of above average intelligence who's tracking conversations and knows what's going on,” Comey said. “I don't think he's medically unfit to be president. I think he's morally unfit to be president.”
"That's not a policy statement. Again, I don't care what your views are on guns or immigration or taxes,” Comey added. “There's something more important than that that should unite all of us, and that is our president must embody respect and adhere to the values that are at the core of this country. The most important being truth. This president is not able to do that.”
What should happen
Many Trump opponents have called for his impeachment, but Comey takes a different view,
The former FBI director, who served for nearly four years, suggested to Stephanopoulos that impeaching Trump would be the easy way out.
"I think impeaching and removing Donald Trump from office would let the American people off the hook and have something happen indirectly that I believe they're duty bound to do directly,” Comey said. “People in this country need to stand up and go to the voting booth and vote their values.
"Impeachment, in a way, would short-circuit that," he added.
Possible long-term effects
While Comey shared his fear of the damage he says Trump is inflicting on the national consciousness, he expressed optimism that it’s not permanent.
"I hope one of the things that comes out of the Trump administration his first term is a recognition that, as much as we fight about those policy issues in this country, what's at the core of this nation," Comey said in the interview.
"We are just a collection of ideas. And at the core of those ideas is that there is a thing called truth. There is the rule of law. There is integrity. Those things matter before any fights about policies.
"People who tell themselves, 'Well, yes, Donald Trump is unethical but I'm getting the right Supreme Court justice or the right regulatory rollback' are kidding themselves because if we lose that tether to the truth, if that stops being the norm at the heart of our public life, what are we? Where are we as a country?
"So I worry sometimes people think I'm talking about politics. Not in the way we normally talk about in this country. But I hope in the most important way. Values matter. This president does not reflect the values of this country," he said.
Comey, who was fired in May 2017 by Deputy Attorney General Rod Rosenstein before Trump later took credit for the dismissal, said there are already positives coming out of the problems he perceives.
He likened the Trump presidency to a "forest fire."
"His presidency is doing, and will do, tremendous damage to our norms and our values, especially the truth. And so that's bad. And terrible things happen in forest fires," Comey said.
"But I'm an optimistic person. And so I choose to see the opportunity in a forest fire because what forest fires do is allow things to grow that never could've grown."
He cited the student-led March for Our Lives campaign as an example of how citizens have become more motivated in the past year, and "that was not happening three or four years ago."