> To replace the agreement entered into during World War II between the US and Denmark, a new agreement with respect to Greenland was ratified on 27 April 1951 (effective on 8 June 1951). At the request of NATO, the agreement became a part of the NATO defense program. The pact specified that the two nations would arrange for the use of facilities in Greenland by NATO forces in defense of the NATO area known as the Greenland Defense Area.

So I wonder what would happen to the treaty/base if the US left NATO?