The man who nearly 30 years ago helped create the myth of Donald Trump has a lot of regrets ― and no small amount of fear over what a Trump presidency would mean.

In a scathing interview Monday with Good Morning America, Tony Schwartz, who co-wrote Trump’s 1987 business best-seller Art of the Deal, blasted the real estate mogul as an attention-deficient man with “sociopathic tendencies” who is a potential danger to civilization.

Schwartz said that among the myths he regrettably helped perpetuate about Trump is the idea that the businessman has a high level of intelligence and savvy.

“I believe he is so insecure, so easily provoked, and not ― not particularly nearly as smart as people might imagine he is. And in the face of someone like Putin provoking him cleverly. ... I do worry that with the nuclear codes [Trump] would end civilization as we know it,” Schwartz told GMA’s George Stephanopoulos.

Schwartz’s harsh rebuke of Trump follows an explosive interview with The New Yorker in which he said “I put lipstick on a pig,” and added that if he were to write the book today, he would call it “The Sociopath.”

Schwartz spent 18 close months with Trump ahead of the book’s publication. He now claims he’s not the book’s co-writer, but a ghostwriter who penned “every word” ― with minimal input from Trump. Howard Kaminsky, the former head of Random House, which published the book, backed up Schwartz’s claim, the New Yorker reports.

Since Trump announced his candidacy in 2015, Schwartz told GMA he “hasn’t slept a night through.”

He’s speaking out now, he said, as a matter of “civic duty.” Schwartz acknowledged some of the likely criticisms that will follow his bombshell statements ― including the fact that he is a lifelong liberal and that he was willing to cash in on his relationship with Trump in the past.

“We had a successful experience together. I never in a million years thought he would run for president. Had I thought that 30 years ago, I wouldn’t have written the book,” Schwartz said.

If Trump is elected president, Schwartz said he will regret writing the book even more than he does now.

“I feel a deep sense of remorse that I contributed to presenting Trump in a way that brought him wider attention and made him more appealing than he is,” Schwartz told the New Yorker.

UPDATE: July 20 ― Schwartz reportedly said Wednesday that Trump had ordered him to stop speaking about the topic this week.

Art of the Deal ghostwriter Tony Schwartz just told @maddow on @MSNBC that Trump has sent him a cease and desist to stop him from speaking. — Mark Kornblau (@MarkKornblau) July 20, 2016

CORRECTION: A previous version of this article said Trump’s book was published 20 years ago. It was published nearly 30 years ago.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.