About 1 in 5 voted for Trump. Millions more voted for Clinton. A few million voted for the other candidates and many millions didn't vote. A big chunk of the Trump voters just wanted a Republican in office. I think the number who voted for him in the primary is worrying, but that's an even smaller proportion. In short, Trump being President isn't so much proof that Americans are dumb, but the forces which led to success aren't conducive to desirable political outcomes.