No one who wishes America ill has to blow up a bomb. That might cause severe damage and rattle us. But if you’re clever and you really wanted to half-kill America—to knock it out for a few months or longer and force every one of our material and cultural weaknesses to a crisis stage—you’d take out its electrical grid. The grid is far-flung, interconnected, interdependent, vulnerable. So you’d zap it with an electromagnetic pulse, which would scramble and fry power lines. Or you’d hack the system in a broad, sustained attack, breaking into various parts, taking them down, and watching them take other parts down.

Or you’d do what the people at the center of a riveting front-page story in this newspaper appear to have done. You’d attack it physically, with guns, in a coordinated attack.

The heretofore unknown story happened last April 16. There was an armed assault on a power station in California. Just after midnight some person or persons slipped into an underground vault near Highway 101 just outside San Jose. He or they cut telephone cables—apparently professionally, in a way that would be hard to repair. About a half hour later, surveillance cameras at Pacific Gas & Electric Co. PCG +0.58% ‘s nearby Metcalf substation picked up a streak of light, apparently a signal from a flashlight. Snipers then opened fire. The shooters appear to have been aiming at the transformer’s cooling systems, which were filled with oil. If that was their target, they hit it. The system leaked 52,000 gallons; the transformer overheated and began to crash. Then there was another flash of light, and the shooting, which had gone on almost 20 minutes, stopped.