To answer my own question after a bit of reading, the answer is that other NATO countries are expected to come to Denmark's aid. That said, the USA had the requirement watered down in the original agreement. Ironically it was only to aid the USA after 9/11 that it has been invoked. Further irony would be if Trump took the USA out of NATO they might strengthen the commitment!
If we so much as step a violent toe in Greenland I sincerely hope that the entire world places steep sanctions and tariffs on the US. We, as a species, need to move beyond these neanderthalic behaviors, and anyone who engages in them needs to be punished severely. An immediate and severe reduction in the quality of life of the American populace may be one of the few things which will motivate us to stop the madness that many Americans decided to plunge us back into.
>Further irony would be if Trump took the USA out of NATO they might strengthen the commitment!
It wouldn't surprise me if he did. Trump seems to believe the US is somehow being swindled and cheated by every international agreement and commitment it has. It's a weird victim mentality for the world's last superpower to express, as if the US didn't force the current order onto the Western world at gunpoint, entirely for its own benefit.