The co-author of Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE’s bestselling book “The Art of the Deal” says he is horrified the billionaire may win the presidency.

“It’s a terrifying thing,” writer Tony Schwartz said Monday on ABC’s “Good Morning America." "I never in a million years thought he would run for president.

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“I haven’t slept a night through since Donald Trump announced for president because I believe he is so insecure, so easily provoked and not particularly nearly as smart as people might imagine he is.”

Schwartz said he has grave concerns about how Trump would handle conflicts with world leaders like Russian President Vladimir Putin.

“In the face of somebody like Putin provoking him cleverly — because Putin’s a heck of a lot smarter than Donald Trump — I do worry that with the nuclear codes he would end civilization as we know it. This is a man who has more sociopathic tendencies than any candidate in my adult life that I’ve observed.”

Schwartz added Trump, the presumptive GOP presidential nominee, lacks the focus needed for the nation’s highest office.

“He has an incredibly short attention span,” he said. "He was unable to do interviews with me past 10–15 minutes. Finally I had to sit in his office and pick up a phone eight feet away from his desk so I could listen in on his calls and turn this into a book. My two-year-old grandson has a longer attention span than Donald Trump."