One reason for Trump's victory is that he communicated in very easy conversational and the sort of bar room language that seemed very different from Obama's intelligent and far more thoughtful use of language. Part of that was to show the US had an intelligent leader after George W Bush.
Of course, Trump himself is not 'dumb'. Early interviews going back to the 1980s reveal him as well and softly spoken, using plain language without the raucous New York accent and intonation he adopted when he became a reality TV star or when advertising 'Trump steaks'. President Trump is a fictional creation made real-by Trump.