The recent film Civil War gives a good example of what could happen. There is certainly a subset of Trump supporters that would follow orders. But a large segment would likely split off and further divide the country.
Greenland’s strategic location in the Arctic is vital for national security, offering control over emerging shipping routes and proximity to the GIUK gap, a critical maritime chokepoint.
Same thing applies to Panama Canal and Canada, which he is speaking about seizing/annexing
It’s likely already too late https://youtu.be/Ufmu1WD2TSk