1. I do not believe that the US will annex Greenland without the consent of the Greenlandic people. Enough with the ridiculous talk of fascism.
2. I do not believe this is within the scope of presidential power without the consent of Congress.
3. It could be that Trump is throwing this idea out there just to get a new and better deal for US bases or stations in Greenland. Would we have earlier warning of an ICBM strike against us? I don't know but there could be valid reasons for increased an US presence.
4. There's no need to get all worked up about this issue. The devil is in the details and we don't know what that is yet.