The US can beef up forces in Greenland now, but Trump's saber rattling could harm relations and put US in an uncomfortable position of resorting to force to keep current assets in Greenland.

The US can beef up it's forces in Greenland if it wants. That just costs lots of money. Current NATO agreements allow that, so I read.

Trump's saber rattling over Greenland could jeopardize those agreements with Denmark and other NATO nations. This could put us in the uncomfortable position of having to resort to force in order to even keep our current military presence in Greenland.