In late January of 1778, the darkest moment of the Revolutionary War, Benjamin Rush wrote to his young wife, Julia: “I thank you for your hint respecting G. Washington, and accept it as a new proof of your affection for me.”

Julia Stockton Rush, who was only 18, had suggested that her brilliant but promiscuously opinionated husband—one of the youngest signers of the Declaration of Independence and now, at 32, surgeon general for the Continental Army’s most active battleground—needed to stop gossiping about George Washington, who was both his commander in chief and his friend. In letters and in conversation, Benjamin was repeating the military backbiting over Washington’s losses the previous year.

In this letter—recently discovered at a small Philadelphia library among a collection of Julia’s longest-hidden correspondence—Rush promised to take her advice. He claimed that so many of the Pennsylvanians in the Continental Congress “speak my sentiments so fully” that he was “satisfied” and would be “silent.” Too late. A disparaging letter in Rush’s hand was making its way into Washington’s camp. The general never forgave him.