This is not an argument for war, but what lies beneath NK's motivations, not Trump at least for now.
It comes down to this. Why does Kim want nukes, why does he threaten with them? Given his insulated dysfunctional view of the world which he apparently believes is envious of him and wants his magnificence destroyed- the West's entire will bent on this objective- because he will otherwise rise to world dominion. Remember he was raised to believe this and had no experience to counter his upbringing.
At this rate Kim will have the means to do more than make threats, he can carry them out in half a dozen years or less.
Perhaps people view this differently and they're right- who knows"
So-
You are President now and you have the resources of the US at your disposal. Given all that you know about Kim, his upbringing, his reactions to diplomacy and threat, what would you do to safeguard ourselves and our allies? Keep in mind that Kim is a potential ticking nuke.
I think by and large countries seek out to develop a nuclear weapons program to deter any potential strong arming from other nations. No one sane will engage another nuclear armed nation because of the potential extinction of the human race.
In what situation could he use nukes against another nation where it does not result in him being vaporized as well ?
The result of nuclear war is the human race going extinct. A fantasy of a post-apocalyptic Rick Grimes with a rifle on the shoulder going out and making it through the disaster is not happening. It will be vaporization in the initial blasts, incineration from the blast wave, blindness from the glare leading to death, death from a lethal dose of radiation within days or from a lesser dose within a longer period and having escaped all that; starvation after the food supply dries up from nuclear winter and radiation contamination.
A nuclear attack against NK would have an effect on other nuclear armed nations. Once the realization comes in that Trump is a complete madman and has just nuked another country, the other nuclear countries will go on alert. I don't see it as being so simple as just nuking one country and expecting other nations to think 'Oh, that's fine, it was just NK', given the unhinged and bizarre behaviour of Trump, other countries would see him as a grave threat following such an attack.
I have my doubts he could initiate an unprovoked nuclear attack without someone saying enough is enough of this imbecile and removing him. Maybe a naive hope, but I'd like to think there are sane and rational people involved in the process from command to action taking place that would stop what could result in the end of civilization.