‘The United States is a republic, not a democracy.” This is one of those oft-repeated expressions that one hears in civil discourse whose meaning nevertheless remains somewhat fuzzy.

After all, the word “republic” — deriving from the Latin phrase res publica, or “the people’s concern” — suggests a measure of popular involvement in government. And the authors of the Constitution were radically republican, at least for their age, believing that the only legitimate form of government was one in which public authority derived entirely from the people.

These ideas surely have some overlap with the notion of democracy, which is …