Sanctions against countries that do business with NK will hurt US consumers and businesses that do business with such countries - and it won't work. Such strategy is to force the NK regime to collapse or a turning on KJU, but China said that they will not let that happen.
KJU is a smart guy and he probably won't do atmospheric nuclear testing, but if he does, the radiation will spread and could cause cancer to people. Anyway, it will be too late after he does it. Off Topic, the US blew up a mosque in Syria, killing men, women and children, breaking international law.