You haven't been paying attention. Trump has been pushing other NATO members (including Denmark) to increasing their defense spending since his first term. It's been a consistent policy and a consistent message for over 8 years now. If you can't see the connection, you're still chasing the squirrel.
It is a confused message, that on one hand suggests Europe needs to spend more to defend itself from a Russian aggressor, that could only invade as far as the eastern end of Ukraine, before it ground to a halt and on the other hand, shows a lot of support and sympathy towards that aggressor. Russia is only a military threat to Europe, with its nuclear weapons. It never could invade, on multiple fronts and capture significant territory and only managed to do so in 1944-5, because of the collapse of the German military, that was fighting on multiple fronts. Even then, it failed to capture Finland. It certainly is not a threat to Greenland.
Europe does not need to spend as much as the US wants it to, on defending itself from the Russians, to defend itself. Even during the height of the Cold War, when it was the Soviet Union, rather than just Russia, an invasion would have ground to a halt in West Germany. It would have been an invasion that played out like the invasion of Ukraine has.
Trump is scared of war and likes to be a peacemaker who should get the Nobel peace prize. He wants Europe to spend more, so it will not have to rely on US help. The only US help Europe needs, is to be able to buy weapons, from the world's largest supplier, a great boost to US GDP, so he should have no concerns there.