Let's turn this around for a second. Let's say we are talking about Putin and Ukraine, or China and Taiwan. If those countries made these same arguments for why they need to invade and take over nearby sovereign nations, the US would oppose them with money, military equipment and even defense treaties.
Ukraine borders Russian territory. There are historical connections between Ukraine and Russia. They even speak a common language, or at least a large percentage of Ukrainians do. Russia feared NATO based on their border. Russia has had its eyes on Ukraine for many years. So how do we make the argument about Greenland that we refuse to accept from Russia about Ukraine?
The same is true for China. The US pumps billions in military aid to Taiwan, which has historically been considered a territory of China. The US bases warships there as well. Yet the US has a defense treaty with Taiwan in the event China invades.
Denmark does not want to sell Greenland. It's their territory. Denmark is a NATO ally. The people of Greenland do not want to become part of the US. They don't even share a common language. They want self-determination by a large percentage - something like 85%. Why would we not respect that? Trump argues we have been trying to obtain Greenland for 150 years. What difference does that make how many years we have wanted Greenland/ It is not ours the Denmark wants to keep it. If anything 150 years of saying "no" should be enough to stop this ridiculous talk about Greenland.