I think there are more nuances to the word than the definition given. It's not the first word I'd think of in relation to Trump. It's one of his secondary characteristics, true. But he's not very good at being supercilious because he's too prone to lapse into jumbled word-salad. To be properly supercilious I think you need a minimum degree of articulacy. Stephen Fry, say, does superciliousness well, if only for comedic purposes.
Also there always seems to be an obvious insecurity not far from the surface with Trump. Again, I don't think that helps put across the full supercilious effect.