Did you think north Korean will be able to attack a building in American even if trump is sleeping? We know that trump has many buildings in usa and international but Kim don't have that capacity you are attributed to him. The highest he can do is attacking American allies who are living at north Korean border.
I see you don't understand the idea. I supposed Kim can infiltrate few agents with bombs on US territory and attack Trump's buildings NOT to kill Trump itself (honestly, it is beyond Kim's possibilities), but to destroy his business and make him poor. Trump really knows how US borders are transparent for illegals, so this threat can be the most effective.
Besides the destroyed house will not stop Trump. You can sacrifice 1000 lives, but save many millions. Which option will you choose?.
Trump is a greedy oligarch. Personal wealth is much more important for him than political ambitions. I think he can even resign from the presidency if have high risk to lose all his wealth.