Carlos Cipolla, an Italian economics historian who taught at Berkeley, wrote "The Basic Laws of Human Stupidity" in 1976.
What Cipolla meant by "stupid," my wife would call "irrational." Cipolla did not mean someone slow witted (who might be slow but rational).
The first law of irrationality, applied to elections, is that we always underestimate the number of irrational voters in circulation. Always.
Irrational people, by definition, make decisions harmful to others and often to themselves. That's how we discover they are irrational.
For example, a man dependent on social security and Obamacare may vote for candidates pledged to end both programs. A woman may support a sniggering rapist for president.
The actions of irrational people cannot be predicted or understood by rational people, Cipolla argued.
Cipolla is not the first to point out that stupid/irrational people do more harm than evil people, who are, at least, predictable.