Most of the people who voted for Trump are NOT stupid. Most of the people who support him now are not stupid either.
They are resentful. They resent most anybody who's not like them who's successful. Trump appeals to them because he comes across like he has the same resentments that they do. His authority as a reality TV star and millionaire, and now as President, gives an imprimatur to their resentments instead of the opprobrium they deserve.
Thinking people despise Trump and say the people who voted for him were not in their right minds. They weren't. Trump was not making rational appeals for their votes. He was making emotional appeals to the darkness inside their hearts. He succeeded in legitimizing the evil that his supporters had kept inside themselves. Now, that evil is the crux of the conduct of his administration.
Hillary Clinton's campaign said that voting for her was the intelligent thing to do. Recall what Adlai Stevenson said to the woman who called out to him during his 1952 campaign, "Governor, you have the vote of every thinking person in America!" But, "That's not enough Madam. We need a majority."
At least 10 million were acting upon their resentments and at least half of Trump's voters -- 30 million people -- had and have an irrational hatred of Hillary Clinton, primarily because of 25+ years of hearing and seeing and believing the propaganda of the Right.
Hillary Clinton's campaign wasted time and money on TV ads trying to convince those 30 million people NOT to vote for Trump instead doing even more work on the ground, including personal appearances by Hillary, to get Blacks and young people in Detroit, Milwaukee, and Philadelphia to vote for her. She failed to make an emotional connection to those potential voters and not enough of them showed up to vote for her. Nonetheless, she did receive 3 million more votes more than Trump, but not quite enough votes to win MI, PA, and WI.