German Finance Minister Wolfgang Schäuble recently quipped to his American counterpart, Treasury Secretary Jack Lew, that he would gladly trade Greece for Puerto Rico. He was referring to the debt crises in both places and indirectly chiding Mr. Lew for offering unsolicited advice. While there are important differences, the Puerto Rican and Greek situations are similar enough to warrant comparison for policy lessons, though perhaps not the ones intended by Mr. Schäuble.

Both are cases of fiscal mismanagement and unsustainable...