The reasonable thing is for Greenland to become independent and enter into a Compact of Free Association with the United States of the sort that exists between the US and the old Pacific Trust Territories we took over from the Japanese Empire when out trusteeship ended and the became independent countries.
It give us all of the defense and strategic advantages of owning Greenland, but allows the Greenlanders to run their own affairs. (And would be cheap compared to buying Greenland even if the Danish government felt it could sell it over the objections of the Greenlanders.) Because of the strategic nature of the minerals that make Greenland interesting, a COFA would let us block hostile powers' access and give US companies the inside track to mining contracts, which in turn would enrich Greenland making them eventually not need to be subsidized as Denmark has been since it shifted from being a full on colonial power with the granting of self-rule to the Greenlanders. And, yes, we'd need to subsidize them for a while, but again it would be cheaper than what Trump's bluster is suggesting. Greenlanders would be allowed to work in the US, be eligible for US social programs, be able to apply for NSF, NIH and other Federal grants (and before any of you complain about that, there are only about 53,000 of them). Pitched right, it should gain the support of Greenlanders, and even the Danish government, which currently subsidizes Greenland to the tune of $783 million/year, about 1% of their national budget, plus defense costs for the island of between 2 and 3 times that much, amount that NRO observes would be rounding errors in the DoD budget.
