The outrage from Hillary Clinton supporters came immediately: Donald Trump might have won the Electoral College, but he appears to have lost the popular vote. This was said to be a violation of democracy, one that defied the principle of “one man, one vote.” A Yale professor slandered the Founders by telling the website Vox that the Electoral College was created to protect slavery.

We can think about this better if we understand two things: What does the Electoral College do, and why does it do it?

On...