The man who co-wrote “The Art of the Deal” said Sunday he believes President Trump’s faculties are diminishing — and that he feels obligated to sound the alarm.

“We are in a true emergency,” Tony Schwartz said on CNN Sunday. “And the accelerated rate at which his breakdown or decompensation is occurring is cause for us, and certainly for me, to come onto TV more often, to tweet more often.”

Schwartz told CNN’s Brian Stelter that he felt comfortable making that assessment because he had “spent an enormous time with [Trump] over a period of 18 months.”

He also said he was a 25-year student of psychology and had spent “an enormous amount of time” with shrinks who were trying to get to the bottom of Trump.

Schwartz said he felt bad for journalists covering the president because they couldn’t go far enough.

“I believe the republic is in enormous risk that goes far beyond what most journalists are comfortable saying and what the general public, therefore — it doesn’t really fully understand,” he said.

Stelter pointed out that Schwartz had inaccurately predicted that Trump would resign before finishing his first year in office.

With the Mueller probe hovering, Schwartz suspected Trump would quit before getting pushed out of office, saying last May, “he wants to figure out a way, as he has done all his career, to turn a loss into a victory. … So he will declare victory when he leaves.”

“You’re right, I completely missed it,” Schwartz admitted Sunday. “I think I underestimated the enormous attachment he would have to being in that office. I think he likes meeting all of these people and he particularly likes dominating these people.”