I think it was a huge mistake for Trump to issued a veiled threat like that to Comey. Comey has said that statement prompted him to have his friend read some of his notes to the press. In other words, Trump had to poke Comey with a stick and get into a p***ing match with him.
The more Trump does stuff like this the more guilty it makes him look. You have to pick your battles if you are smart. This was not the mountain for Trump to die on.