Last week, a Federal District Court overturned the Financial Stability Oversight Council’s (FSOC) designation of MetLife—the nation’s largest insurer by assets—as a systemically important financial intermediary (SIFI). Until the Court unseals this decision, we won’t know why. If the ruling is based on narrow grounds that the FSOC can readily address, it will have little impact on long-run prospects for U.S. financial stability.

However, if the Court has materially raised the hurdle to SIFI designation—and if its ruling holds up on appeal—“too big to fail” nonbanks could again loom large in future financial crises, making them both more likely and more damaging...