you are aware that he doesn't actually believe that he "[...] could have convinced [..]"

it's a manner of speech

a instrument of telling a story

a way to express how completely absurd "US getting involved into Greenland" is for anyone who understands the land (geography/weather) and people even unrelated to geopolitical aspects like alienating allies

My argument stands whether the author meant to be read literally or not. Below the surface it’s still about the tension of rationality and irrationality within social settings.