Americans again mourned the 2,977 people murdered on Sept. 11, 2001. At the Pentagon, President Donald Trump renewed the nation’s vow never to forget and said America must be “strong” and “smart.” That vow asks more of Washington than remembrance. It requires the imagination to prepare for dangers that will not look like the last one.

No technological breakdown belongs on the same moral plane as deliberate mass murder. The relevant lesson of 9/11 is institutional. The 9/11 Commission organized its central findings around imagination, policy, capabilities, and management. It showed how grave danger can grow inside gaps between agencies, authorities, and assumptions long before the public sees a catastrophe.