Former FBI Director James Comey shot back at President Trump’s suggestion that he should be imprisoned, saying the president threatening a private citizen with jail is “not normal.”

“President Trump, I don’t follow him on Twitter but I get to see his tweets tweeted, I don’t know how many, but some tweets this past couple of days that I should be in jail,” Comey told NPR in an interview published Tuesday. “The president of the United States just said that a private citizen should be jailed.”

“I think the reaction of most of us was, ‘Meh, that’s another one of those things.’ This is not normal. This is not OK,” Comey continued.

The president on Sunday proposed “jail” for Comey in a series of tweets in which he also referred to “Slippery James Comey” as a “Slimeball!” and the “WORST FBI director in history.”

Comey, who is on a media blitz for his best-selling tell-all, “A Higher Loyalty: Truth, Lies and Leadership,” which hit bookstores Tuesday, urged voters in the NPR interview not to allow Trump’s “threats to the rule of law” to go without a response.

“There’s a danger that we will become numb to it, and we will stop noticing the threats to our norms. The threats to the rule of law and the threats most of all to the truth,” Comey said.

He said Trump’s attacks on the Department of Justice carry the same perils.

“Lady Justice can’t be peeking under the blindfold to see if Donald Trump wants her to convict so-and-so and not convict so-and-so. If we lose that, we’ve lost the rule of law, and so there’s great danger in the president of the United States saying, ‘You should be in jail,'” he said.

Trump fired Comey, who was at the time overseeing the investigation into Russian meddling in the election, in May 2017.

A week later, special counsel Robert Mueller was named to continue the probe.