In my exchanges with various Americans on social media, it's become clear that the problem isn't that Americans can't find Greenland on a map. They can; Greenland's hard to miss, especially on a Mercator projection. The problem is that too many Americans can't find Denmark on a map. They have no idea what it is and have no real understanding both of the value of allies in general and of Denmark in particular. They don't believe me when I tell them that European allies are worth having, that they do have militaries, that they do enhance our security, and that, in general, they are good for our well-being as Americans.
So, for example, when I say the Danes fought in Afghanistan, they dismiss this because of the assumption that Denmark's contribution was of no consequence, nor, to be frank, was that of any NATO ally. They simply are unaware of anyone else doing anything.
When I tell them that having an ally in control of the Straits of Denmark is a huge advantage, they shrug their shoulders. The Straits of what? Why does being able to bottle up the Baltic Sea matter? It's so remote it might as well be Middle Earth.
When I tell them that Denmark has committed to defending Latvia and keeps an armored battalion there, they have no clue why that might do America any good. They just see (because Trump pointed it out) that Denmark has left Greenland undefended. The fact that Denmark in effect has chosen to defend Greenland by putting troops forward (Latvia) does not compute. And of course they have no idea that since 1941 the US and Denmark have had an understanding about Greenland's defense, which has encouraged Danes to focus east, not west.
And so, when I say that Trump is in danger of killing NATO, they really don't understand why any American should care, since, as far as they are concerned, only the United States does anything, and the rest of NATO is there as window dressing. You (hopefully) and I know that's not at all true, but too many Americans view things in this way.