He can't turn it off because it's in his nature. He can't turn it off when it's damaging politically rather than helpful, as it was when he dispatched all those Republican challengers. As I said yesterday, Trump is profoundly insecure and emotionally needy and is clearly a pathological liar. Given his long history of scams, exaggerations, business failures, frauds and more and the escalating press scrutiny of so much of this history ... well, it's not going to be pretty at all.
Trump has spent his entire life surrounding by yes-men and enjoying a generally fawning press. Relentless scrutiny, even occasional scrutiny will bring out his driving grievance and desire for vengeance in its worst possible light, all about himself, hiding his misdeeds and attacking anyone who questions him.