I don't recall hearing Trump refer to himself as a "populist." Rather, identification of Trump as a "populist" represents a "tag" assigned by another, in this case Professor Muller. As a #populist, Trump becomes open to demonization, as demonstrated by Professor Muller's litany of evil behaviors one should expect from a #populist.
My Princeton education stressed balanced analysis from which we could draw a conclusion (hopefully well reasoned). Unfortunately, Professor Muller's article contains a string of conclusions with little serious supporting analysis. In 1960, this paper would have received 5+ or, at best, 4-.