Thing is the U.S. already has the right to expand its existing bases in Greenland so there is no need for them to take over for security reasons as they can just beef up bases they have.
As for resources the Greenland and Danish governments have said U.S. companies are welcome to bid for mining rights so can get access to to resources so again no reason (other than Trump hates paying for things) for them to control to Greenland.
This isn’t about security or resources but ego for the fat orange fascist. He wants to be first US president since McKinley to expand U.S. territory.