Donald Trump’s onetime ghostwriter, Tony Schwartz, told CNN on Monday night that he is advising Hillary Clinton’s campaign for free, in an effort to make up for having contributed to Trump’s rise to fame in the 1980s.

“This is my penance for having created a man who has become a monster, and I’ve spent 30 years feeling bad about it,” Schwartz said. “Now I feel like I’ve got to show that there’s nobody behind the curtain.”

Schwartz was the ghostwriter on Trump’s first book, The Art of the Deal, which went on to become a best-seller. He spent over a year working closely with Trump on the book, and got to know the businessman well.

He has been one of Trump’s most outspoken critics ever since the real estate mogul announced his presidential campaign.

Schwartz paused when CNN asked him to name one thing about Trump that he found appealing.

“There was nothing I found appealing,” he said. “This is a man who I really believe lacks a conscience at the deepest level, so there really was nothing. He was effective in certain ways, he’s a dominant, aggressive personality and he pushes and he pushes and he pushes and he gets a lot of what he wants.”

Trump’s attorneys threatened to sue Schwartz for defamation after The New Yorker published a profile of him this summer.

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.