NATO is the best way to defend Greenland.

NATO has been a real important alliance which includes Greenland. The US has had a good connection with Denmark and other NATO countries which allows more US military assets in Greenland if the US were to want this. Beefing up military presence in Greenland does cost money so it could be a difficult move given budgetary constraints. Friendly relations with NATO countries has been good for our security. We can't really afford to create sour relations with NATO allies.