Best I can tell, no one is preventing Canada from doing it instead.
Here's the goal posts.......................................................................and here's where they end up.
It doesn't matter what Canada would do, or what I want them to do. My basic point was that despite attacking Obama for doing a "bad deal" with Iran (that was actually fairly fantastic given circumstances), Trump's here would be worse. Why? Because he's giving the other side exactly what they want, for free, and without any concessions.
If you were to ask what NK wants, its number one goal is for America to leave SK and abandon its security guarantees. The US, under Trump, would be giving that up without any kind of compensation or concession.
As for the guarantees, the cost to the US is trivial compared to:
a) Maintaining Korea as a trading partner;
b) Offsetting the power of China in the region; and
c) Maintaining global stability.
That last factor is why Trump's ideas are most imbecilic. Global stability is good for those on top. The higher up the food chain you are, the more you should support and maintain international structures and geopolitical stability. Geopolitical chaos gives rise to many new risks, and presents current "have nots" with opportunities they'd otherwise have. There's a reason why Rome and the UK prospered when Pax Romana and Pax Brittania ruled. There's also reasons why those systems collapsed when stability was shaken by outside factors (such as plagues, mis-management, and short-sighted cost savings at the expense of long-term planning), and led to the collapse of those Great Powers.