I wonder how likely Trumps assumption, that Russia or China will take it if he doesn't, is..
If serious: agree, Russia or China won't take Greenland.
2. Russia can't even expand their presence to Ukraine (not a NATO memeber).
3. China has no access.
So, 0%.
Because controlling Greenland means whoever has it gets excessive control over the Arctic Sea. And both parties, but especially Russia, do not want a party like the United States to have this amount of control given the Arctic is in their backyard.
The US had military bases in Greenland when Soviet nukes had to be delivered with bombers flying over Greenland.
When ICBMs became a thing, those bases weren't as important anymore.
Something you can already see in Venezuela as we speak: The Trump Administration has essentially blocked countries like Russia and Iran to ship oil from Venezuela.
If they capture Greenland and can build a big Naval presence there they are in a great position to confiscate every cargo ship destined to Russian harbors in the north, and close off China's trading route in the Arctic aswell.
What's the problem? Denmark would have welcomed a big Naval presence in Greenland. It benefits them too.
It should have been:
America: can we have a big Naval base in Greenland?
Denmark: sure. 100 year agreement?
America: give us big Naval base in Greenland or we will annex you!
Denmark: Eh... sure, are you alright?
America: we will annex you.Russia and China are just made-up excuses for Trump to do what he wants to do: steal territory, at gunpoint if needed.
OK, great, they've got troops in Greenland. Now they have to keep them supplied. How are they going to do that? Well, either through the air or by sea.
Does either have a navy that can do that? No. Does either have an air force that can do that against US opposition? No.
So it's really unlikely. Even if China or Russia were stupid enough to do that, they could never hold it.
Now, perhaps the more interesting question: How likely does Trump think it is? Does he think it's real, despite the absurd impossibility of it? Or is he just saying fact-free stuff that he hopes some people will believe?