The Art of the Deal' co-author says giving Donald Trump the nuclear codes could 'lead to the end of civilization

"Good Morning America"/ABC

"The Art of the Deal" co-author Tony Schwartz appears on "Good Morning America" on Monday, July 18.

When presumptive Republican presidential nominee Donald Trump announced his candidacy 13 months ago, he proclaimed, "Our country needs a truly great leader, and we need a truly great leader now. We need a leader that wrote 'The Art of the Deal.'"

He was referring to his 1987 memoir, which offers some insight into his personal life but mainly focuses on the philosophy to which he credits his success in the real estate industry. The business guide sold over one million copies and has been one of Trump's talking points over the past year, a symbol representing his deal-making prowess.

But on Monday morning, the first day of the Republican National Convention in Cleveland, the book's co-author Tony Schwartz came out blasting Trump. In a newly published New Yorker article by Jane Mayer, Schwartz - who is the president and CEO of the Energy Project consulting firm - said that not only did he write the book with practically no help from Trump, he feels ashamed to have contributed to the success of someone he now considers a monster.

"I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilization," Schwartz told Mayer.

This is not the first time Schwartz has weighed in on Trump. Last September, after seeing Trump repeatedly refer to "The Art of the Deal" for three months, Schwartz tweeted:

In the publishing world, it's standard practice for ghostwriters to lead writing projects for celebrities - it's how athletes, movie stars, and executives can publish 300-page books with no prior book experience and relentless schedules. These working relationships can range from the ghostwriter doing all of the writing after conducting extensive interviews to serving as editors who liberally work with rough copy.

On the cover of "The Art of the Deal," Tony Schwartz is given credit as co-author, as opposed to being tucked into the acknowledgments section. But he's taking offense at the way Trump is portraying himself as the actual lead writer of the book, a claim he maintained with The New Yorker.

Schwartz spent 18 months shadowing Trump in the late '80s and interviewing his family members and associates in order to capture Trump's voice. It was these experiences, he now says, that have made him conclude Trump is unfit to be president.

Schwartz told "Good Morning America" host George Stephanopoulos Monday morning that Trump has "an incredibly short attention span" and that he isn't as intelligent as his supporters think he is.

Stephanopoulos mentioned that critics are saying that Schwartz is only speaking his mind now because he already made millions of dollars in royalties, and that as a self-proclaimed liberal and Democratic donor, he has an agenda in this election.

"You know, I do have an agenda," Schwartz replied. "And the agenda is about Donald Trump's character. It has nothing to do with his ideology. He has no ideology. He's not a person who has beliefs, except the belief that he himself should prevail in the end."

He added that he never mentioned any of this before because the two enjoyed the results of a successful project and that he never expected Trump to run for president, let alone to become a nominee. "I now feel it's my civic duty," he said. "I have nothing to gain from this."

You can read Mayer's article at the New Yorker's website and see the GMA clip below.