‘Art of the Deal’ co-author worried an ‘emboldened’ Trump may target him personally for revenge

Thirty-five years ago, author Tony Schwartz began interviewing Donald Trump as preparation to ghostwrite an autobiography for New York City business scion.

The result was the 1987 bestselling book Trump: The Art of the Deal, for which Schwartz received co-author credit.

In the decades since, Schwartz has become a frequent critic of Trump. He is an MSNBC analyst who has a re-occurring feature on "The Beat" with Ari Melber titled "State of Mind," in which Schwartz dissects the president's mental state.

With Trump now seeking retribution against all those who have crossed him, Schwartz is worried he may be targeted.

"The degree to which Trump feels emboldened to exact revenge on his perceived enemies is truly frightening -- to me personally, but also for all of those he may go after," Schwartz posted Thursday.