I suspect that trumps contribution to North Koreas change of heart was that the Chinese could use him as the Mad man ' in the Mad man theory.
Ie this guy is nits and really might nuke you- as we live next door thats not good for us so sort things out with the yanks or we will sort you out .
Israel is just a votes issue, a powerful lobby in USA in some very key areas, like NY and LA. Squeeze Israel and we will vote for the other guy .
As for keeping promises -Hitler did that to a large degree especially right after he got elected-that worked out really well for Germany didnt it