The interview came ahead of the April 17 release of Comey's book "A Higher Loyalty: Truth, Lies, and Leadership."
Click here to read the full transcript of the interview.
Before the interview aired Sunday, the president tweeted about Comey, calling him "a man who always ends up badly and out of whack (he is not smart!)"
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!— Donald J. Trump (@realDonaldTrump) April 15, 2018
Comey dug deeper into a variety of subjects, including concerns over whether the Russians have something to hold over Trump and how Comey handled the Hillary Clinton email saga.
The ex-FBI director also spoke about what he believes makes the president unfit to hold office, but not for the reasons people may think.
"I don't buy this stuff about him being mentally incompetent or early stages of dementia," Comey said. "He strikes me as a person of above average intelligence who's tracking conversations and knows what's going on. I don't think he's medically unfit to be president. I think he's morally unfit to be president."
Here are five of the top moments from the interview.
1. Comey was nervous when he was about to meet Trump
Comey met Trump in person in January 2017 during the presidential transition.
He said that the president lived up to his expectations, at least on a physical level.
"He had impressively coiffed hair ... it looks to be all his. I confess I stared at it pretty closely and my reaction was 'it must take a lot of time in the morning,'" Comey said.
"His tie was too long as it always is ... he looked slightly orange up close with small white half-moons under his eyes, which I assume are from tanning goggles," he said.
One of the main reasons for the meeting was to talk to Trump and his team about Russian meddling in the 2016 presidential election.
Comey added that then president-elect Trump's first question was to confirm the alleged meddling had no impact on the election and that "the conversation, to my surprise, moved into a PR conversation about how the Trump team would position this and what they could say about this."
Comey said the interaction reminded him of his past work prosecuting mafia bosses, suggesting that everyone, including the intelligence agency, were all working as part of the same team - or in mafia terms - part of the family.
Trump and his team have repeatedly attacked Comey's credibility.
James Comey is a proven LEAKER & LIAR. Virtually everyone in Washington thought he should be fired for the terrible job he did-until he was, in fact, fired. He leaked CLASSIFIED information, for which he should be prosecuted. He lied to Congress under OATH. He is a weak and.....— Donald J. Trump (@realDonaldTrump) April 13, 2018
2. Email saga presented "no-win situation"
Comey said he knew the investigation into former Secretary of State Hillary Clinton's use of a private email server would be a "no-win situation" for him.
Despite criticism from Clinton opponents, including Trump, for not bringing Clinton before a grand jury, Comey defended his decision during the interview.
"We would prefer with a subject of an investigation to do an informal interview. Lot more flexibility there," Comey said, adding that "they're still required to tell the truth."
Comey also said he had concerns about then-Attorney General Loretta Lynch, who reportedly asked him to call the email saga "matter" and not an "investigation."
The former FBI director said he would still send the Oct. 28 letter announcing that the FBI was looking back into the Clinton investigation days before the election even if it meant that the letter would elect Trump.
"Down that path lies the death of the FBI as an independent force in American life. If I ever start considering whose political fortunes will be affected by a decision, we're done. We're just another player ... in the tribal battle," Comey said.
3. Dinner with a deal on the side
In Sunday's interview, Comey detailed the 'loyalty' conversation he said he had with the president during a dinner at the White House.
"He said, 'I expect loyalty, I need loyalty.' And I just stared at him and had this little narrative with myself inside, saying, 'Don't you move, don't you dare move. Don't even blink,'" Comey said.
Comey said that he couldn't think of anything to say in response to the president at first. However, Trump again emphasized he needed loyalty.
That's when Comey says he told him "You will always get honesty from me."
4. Reading into Trump's alleged request
Comey explained that the next uncomfortable moment came on Feb. 14, 2017, the day after then-National Security Adviser Michael Flynn had been forced out.
He said that Trump asked everyone to leave after a security briefing, leaving him and the president alone.
Comey said Trump "said he hopes I can let it go," referring to the criminal investigation into Flynn.
Trump has denied saying this.
Comey told Stephanopoulos Sunday that he didn't stop the president from making a request, but added "maybe I should have."
5. Could the Russians have something on Trump?
When asked about Russia and Trump, Comey said he isn't sure if the special counsel will find anything on the president.
"I think it's possible. I don't know," Comey responded. "These are more words I never thought I'd utter about a president of the United States, but it's possible."