Kim may only know what he is told about US politics. Maybe he's been told that the Democrats will impeach and remove Trump next year and thinks that would mean that Hillary became President...who would give him whatever he asked for (for a suitable donation to the Clinton Foundation).
Or at any rate expects the Democrats to win in 2020 so he just needs to stall until then.
Depends, can he hold his country together that long?
A starving army is not a ready army, think about it