If Trump were not so convinced that he is not only the smartest person in the room, but also knows everything relevant to every area of policy (the first might often be true, the latter is a complete delusion), we'd probably already have sweet-talked the Greenlandic independence movement into leaving Danish sovereignty and forming a Compact of Free Association with the United States: we'd get full control of their security and enough control of their economic affairs to prevent hostile powers from accessing Greenland's resources, they'd get more development aid than the Danes now give them, full control of their internal affairs, and for their citizens the sort of access that citizens of CFA countries have to US programs (e.g. eligibility for NSF grants).
But no, Trump has to propose trampling on the Greenlanders right to self-determination (recognized by the Danes) with offers to buy their country from Denmark, or destroying NATO by attacking another NATO country.
It might be less maddening if Trump were stupid about which problems face America, rather than correctly identifying them, then proposing or even imposing completely dumbass "solutions". (And yes, a weakly defended Greenland with the potential to accept Chinese business interests is a problem facing America.)