Former FBI Director James ComeyJames Brien ComeyBiden is the least electable candidate — here's why Top Mueller prosecutor Andrew Weissmann lands book deal Trump to appear on 'Meet the Press' for first time as president MORE said Sunday that Democrats "have to win" the 2020 presidential election to stop President TrumpDonald John TrumpConway defends herself against Hatch Act allegations amid threat of subpoena How to defuse Gulf tensions and avoid war with Iran Trump says 'stubborn child' Fed 'blew it' by not cutting rates MORE from lying from the White House.

"I can tell you that all of us should use every breath we have to make sure the lying stops on Jan. 20, 2021," Comey told ABC News, referencing inauguration day after the 2020 presidential election.

"I understand the Democrats have important debates now over who their candidate should be ... but they have to win," he added. "They have to win."

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Comey warned that the country can't "become numb" to Trump's behavior because it would alter its norms and foundations.

"We have to remind ourselves that the president of the United States of America is publicly announcing that people are committing crimes, they should be in jail — private citizens — that's not OK," Comey said.

The former FBI director reiterated his belief that Trump should not be impeached, because doing so would let "the country off the hook." 

Comey and Trump have frequently clashed since the president fired Comey in May 2017. The president has labeled Comey a "liar" and a "leaker," while the former FBI chief has said Trump is "morally unfit" for office.

Comey last week testified before a pair of House committees, where he shared that the counterintelligence investigation into possible conspiracy between Russia and the Trump campaign began by examining four Americans.

He did not identify the individuals, citing the potential that they are part of an ongoing investigation, but he did note that Trump was not one of the four individuals.

Trump lashed out at Comey on Sunday morning, accusing him of lying in his testimony.

Comey called the president's tweet "disturbing."