If a foreign power blew up a powerline by software, VS gentlemen in balaclavas with semtex VS uniformed troops in Heinekels - we don't currently have the army deal with those.
If the power line has been destroyed then there is not a lot that can be done to prevent it without some sort of time travel capability.
But preventing it from being destroyed before the event means people working at the power company looking for intrusion attempts, and people working for the manufacturer of the hardware manufacturers examining it for vulnerabilities. Repeat thirty thousand times across industry, commerce, local government, healthcare etc. I don't think this is really a job for the military.
Biting the hand that feeds IT
