Well, Trump never said he promised peace. He is showing NK the door, but like Neo from the Matrix he can't make them walk through it.
I think Trump had to try the diplomatic route. If Trump is forced to bring military force to bear his critics on the Left would hammer him for not giving diplomacy a chance. Now that he has done that, he has shown the world that he reached out in an effort to bring a peaceful solution to the problem. Now, having been deceived and rebuffed, Trump is justified in lowering the boom on the Norks if they start trying to intimidate us again. I think he handled the situation well.
Well, you can lead a horse to water, but you can never go home again.