We could very well end up in a situation where we have the US and Russia working together to destabilize the EU, perhaps European leaders fear this and will let Greenland go.
I included the economic disaster in my list. I just felt that I needed to explain why I considered it a military disaster even though the US could likely "win" Greenland. It would lose Europe and the ability to project military power through Europe. This impacts the ability to project power in Africa and the Middle East. It'll lead to a cascading military failure which leads to lots of other problems including further economic problems.
And they should also consider all equipment, munition and weapons stored at those facilities, including the B61 nukes, null and void. Because their former NATO allies will never ever allow the US to take equipment which could be used against them later on back home.
And if they come with the argument "But that is against international law", they should have thought about that before illegally abducting a foreign president from a country at peace according to those same international laws.