This US obsession with Greenland and Denmark seems to be the most random, our of left field thing.
Denmark don't do anything but export salamis.
As Climate change continues to lessen sea ice, this trend, if not stopped will open up the Northwest passage shipping lane.
The NorthWest passage would substantially reduce the value of the Panama and Suez Canals as major routes to much of the world sea transport allowing ships much shorter travel time generally and not having to cue up at costly canal and lock systems.
Currently the countries with the strongest territory claims on the Northwest passage are Canada, Russia and Greenland/Denmark.
This is entirely why Trump and the US see it as so strategic as they have no plans to try and slow the effects of climate change and want to ensure they will be the biggest beneficiaries of it.
Beyond that and why Trump muses about taking over Canada is that overall Canada is predicted to be one of the biggest beneficiary of climate change, with the least harm. The border areas of Canada, near the US rising in temps may see them replicate a more normal 'Florida' type temperatures. Desired by many. But vast, vast regions of Canada's north, historically unliveable are now currently opening and are very resource rich (water, lumber, minerals and oil) and that is only going to continue.
YOu can absolutely predict a future where you can draw a line in the US below which water, drought issues, extreme weather and other issues will see people needing to migrate out while at the same time Canada is looking to populate vast areas of now open arable land to generate tax revenue from.
Would Canada open up for a Land Rush type grab for Americans and others willing to move and settle our North, in the way the US West was settled? Would Canada then become the economic power in North America, over time, with the bigger population and mass resource wealth?
There are many US think tank papers discussing just this, which is why Trump and those who back him have the wet dream of locking Canada and Greenland down as US States so it is the US gaining all that benefit and not falling in stature over time.