It started last week with his attack and lies against a Flint, Michigan pastor. It continued with crazed Birther press conference, his suggestion that Hilary Clinton should disarm her body guards and "let's see what happens", went after a New York Times reporter suggesting she was mentally ill (projection much).
The birther story in particular, Trump and his allies have no defense. Trump continued to promote the story even after Obama released his birth certificate. And it's been beyond debunked that Clinton had nothing to do with starting the story. Those are facts.
But also, in particular, he seems to have really ticked off the media. Which, possibly, could be bad for him if they stop paying as much attention to him in the way he wants. The "look at me" press that Trump likes could instead become impartial objective press not concerned with his Reality TV approach and start actually pressing him for real answers, that he doesn't have.