Both NK and Iran are clients of both Russia and China (to varying degrees).
A good president would have it be discretely known by China and Russia, that an EMP attack that hits the US will be treated as a nuclear attack by the combined forces of Russia and China. An attack which takes out our infrastructure, with anticipated deaths in the millions would result in our expending our entire land-based nuclear missile arsenal against both China and Russia. It would thus be in the interests of both China and Russia to do something about NK and Iran.
You are correct. Sadly, the past 4 administrations have coddled the NK’s and been mute about the reason NK exists at all.