We do know (from press reports) that the President has been getting China to cooperate on trade with NK. Are those reports correct, and has China not cheated? I don't know, but if you recall when Chinese and NK oil tankers were caught doing oil transfers on the high seas, you might agree that the U.S. administration is probably keeping good tabs on that. Evidently they (China, DPRK) must be taking Trump seriously. How seriously is yet to be seen -- there is not yet a deal, and we'll have to see, for perhaps they are still trying to play the U.S., and the Administration might fall for whatever Xi and Kim have in mind.

Starving NK can definitely be arranged. First you make sure they cannot trade, then you wait for things to get bad. The NK economy will not thrive and almost certainly will go south. As to how much starvation is needed for regime change, I don't know, but unlike Clinton and Bush, Trump can be believed that he'll not buckle, and that he'll provide no food aid.