In my opinion, he is more interested in what lies beneath Greenland's soil, even though he cannot extract it himself and even though doing so would have consequences for the environment, which all countries are supposedly so concerned about. If there were nothing to be found in Greenland's soil, he would have lost interest long ago. Raw materials are what matter to him, and that is something that America, the major consumer, does not have. Apparently, conserving resources is not important there, unlike in other countries. The idea that the ice cap would melt and therefore make it easier for Russia to reach America is, of course, nonsense. If America really felt threatened, which is not surprising given that it has so many enemies, it would have been attacked long ago. The reverse is also true, of course. Why doesn't Russia say, let's take Greenland, because America is very close by with a melting ice cap? Incidentally, that melting ice cap will probably not be as bad as predicted, because a few years ago, The Times magazine reported that a new ice age was coming. And now we suddenly have to worry about global warming of 1 degree over x number of years.
Trump is a whiner, in any case, and there are a lot of cartoons circulating at the moment. After the severely demented Biden, this is not really an improvement, but he may think that this is also publicity for him and he likes to be flattered. The overall picture people have from the USA is not a good, let alone a good one.