Primates, especially humans, are very, very good at the facial communication:
Expressing information through facial expressions
Interpreting information expressed facially
Distinguishing real from fake facial information
As with any evolutionary adaptation, there is a range of degrees. For example, there are real, heart-felt smiles, and there are fake smiles. Donald Trump seems to know only the latter. He thinks a smile is to make a face like he is about to pronounce a word that begins with the letter F, or the sound SH. What about Mike Pence? He seems to smile only with great difficulty, making it hard to tell if his smiles are real or fake.