Exactly what Russia did in Ukraine.
But that doesn't mean the guy is not doing it. The option is there.
One thing we don't know yet is whether US intelligence knows something we don't, in terms of China and or Russia.
USA has since 1942 I believe had the military defence over the island, so in that capacity its not something new.
We’re in the midst of the collapse of the rules-based international order. America ignored it in Iraq and Libya. Russia ignored it in Chechnya, Georgia, Moldova and Ukraine. China is ignoring it across the South China Sea, Hong Kong and Tibet. (For brevity I’m largely ignoring the Middle East and entire continent of Africa.)
The only ones holding onto the system for dear life are the Europeans, and even there they’re starting to wise up. I’m not thrilled about what’s to come. But it’s clear that just because annexing through force is de jure illegal doesn’t have much bearing onto whether it will happen.
Isn't it a matter of resource mining? Greenland is getting warmer and thus the access to its resources becomes gradually easier.
In context, with talking about using "economic force" to force a US "unification" of Canada? I'm less likely to give him the maximum benefit of the doubt.
The US also engineered Panama's independence in order to get sovereignty over the canal zone, which they completed. And then of course they actually invaded the country in 1989.
That's not what happened. In fact its local government reached out to the US and agreed to come under its wing as a de-facto protectorate, which it saw as a preferable alternative to Canadanian/British (and in any case German) intervention.
So the idea is clearly not new.
Now, this is Trump so a lot of bluster and unclear what he is actually getting at but in an historical perspective neither this nor (re)gaining control of the Panama canal (which the US only fully relinquished in 1999) are new or crazy.