Last week, The Post reported that Paul Horner, “the 38-year-old impresario of a Facebook fake-news empire,” believes he turned the election in favor of Donald Trump. For many, the claim signals an alarming turn into uncharted political territory. But fake news is part of American history. In fact, it goes back to the founding of the republic.

In 1769, John Adams gleefully wrote in his diary about spending the evening occupied with “a curious employment. Cooking up Paragraphs, Articles, Occurrences etc. - working the political Engine!” Adams, along with his cousin Sam and a handful o...