Donald Trump is no moron; he just plays one on TV. He spouts vile nonsense, but even his most ardent detractors concede that he is one clever dude – diabolical, calculating and shrewd.
Does he promote stupidity only to win over the dumbest and the vilest voters, the Republican base? That would be the most likely explanation. He seems to have figured out what they want to hear, and he is feeding it to them by the carload.