After a thunderstorm arrived on July 4th, when the National Mall was crowded with visitors, local officials initiated their sheltering plan. See: Initiating ‘Safe Haven’: 200,000 July 4 revelers get shelter from the storm.

It wasn’t a drill. It was happening, and now: Open the doors, suspend the bag checks, turn off the magnetometers, let everyone inside.

The plan had been developed to shelter masses gathered on the Mall in the case of an emergency weather situation, but the evacuation ahead of Saturday’s Independence Day celebration also signaled what might happen in the face of a terror threat: “Operation Safe Haven.