I'm the kind of person who, for example, doubted the Covington Kids story from the beginning. By which I mean I'm not particularly alarmist about a putative vast right-wing catastrophe taking place. But any popular leader (and he's very popular among the people he's popular with) can start incidents like that by accident.
Imagine what effect that would have on already-pressured populations across the globe.
had escalated more, I don't think it's too far-fetched to imagine an unstable dictator sending off a nuke after being goaded on twitter.
I think it's within the realms of possibility at the very least, although very unlikely (mostly because NK hasn't got a decent delivery system, their nukes aren't very advanced/portable yet and Kim Jong Un's probably not too keen for NK to be destroyed in retaliation).
Given Trump's recent tweet of the spy satellite image, and the apparent taunting of Iran, it's also possible that type of thing could be responsible for triggering future terrorist attacks (although obviously that's not millions of people).