Electricity is the key infrastructure underlying our society, and moreover, the most vulnerable. It is the target, even if most people don’t know it yet.
People need air, water, and food.
Saddam Hussein showed the limits of poisoning the air. He had no moral qualms holding him back. But he only did it to limited effect over a limited geographic area a handful of times (against Iranians and his own citizens). He did not conquer enemies with sarin.
The important factor to understand about our water and food supply, is that they are relatively decentralized.
Texas has almost 200 “major water-supply reservoirs.” California has over 1,000 reservoirs and there over three dozen mega-reservoirs.
Food supplies are even more decentralized than our water supply. For instance, look at a weak point, centralized factory farming, by the biggest company Tyson. But even they have over 100 facilities spread out over more than half our states and also contract with independent providers. And Tyson is just one supplier of some food types out of many, many more providers.
True, attacking our air, food, and water, would cause massive panic, huge economic costs, and it could cause a significant number of deaths. They are good targets for terrorists who wish to provoke a response.
However, these are not existential threats to our existence. They are too decentralized. There is no way to destroy America by striking these targets.
But what about an enemy whose goal is to maximize damage done? Like happens in actual war. What would they attack?
Our electric grid.
There are only three electric grids in continental America. Each one is a system of connected transformers and wires moving energy from power stations to houses and businesses.

A problem in one place on the power grid, can mean no electricity hundreds of miles away.
In 2003, a tree branch hit a wire, a company monitoring the grid failed to act, and the problem cascaded into a a multi-state blackout for 55,000,000 people lasting hours and days.

People don’t have an instinctual connection with electricity, and thus there is no deep emotional fear of this scenario. An attack on our electrical grid would be an excellent attack for an entity who wants to do serious damage to America, but doesn’t want to incur our wrath.
Think this through.
We only have water and food, on the scale needed by modern society and distributed to local stores and homes, because of electricity. With no electricity, there is no running water, modern farms, refrigeration, supermarkets, restaurants, treatment plants for water, or gas pumps.
True, we could revert back to traditional farming communities. But with 8.5 million people in NYC and 80%+ of Americans living in urban areas, what do you think would happen in the near future?
The electric grid is vulnerable to attack.
Though it may appear resilient because it occupies a wide geographic area, keep in mind the blackout of 2003. There are a few methods to attack it.
Firstly, a computer virus could be injected into the system. In fact, some originally thought the 2003 blackout was caused by a hacker attack (how do we know for sure it wasn’t?). A company which monitored the power lines and distributed power along them to prevent surges and failures didn’t do its task due to an alleged bug.
So, one avenue for attack, would be to introduce a bug into the power stations and the companies that distribute the power along the grid to create a similar cascading failure.
Another avenue for attack is on the transformers which step the voltage up and down to send it big distances on the wires. The extra high voltage transformers we use are huge, weighing up to almost a million tons. America doesn’t build them anymore but imports them. They take months to build and then are so big they have to be shipped by special rails to their destination.

They are absolutely critical to our grid. They are not protected from attack, neither by virus, nor physical attack, nor nuclear EMP attack.
Transformers are the king of centralization: “According to the WSJ, a classified U.S. FERC study concludes if just 9 of the 2,000 extra high voltage transformers in the U.S. were damaged (0.0045% of all EHV transformers) a nationwide blackout would result, lasting 18 months.”
These transformers could be taken out with physical sabotage. In 2013, “a sophisticated assault” involving numerous highly trained gunmen took out transformers in California. The Metcalf Sniper Attack.
Another way that the attack could occur is via nuclear EMP. A nuclear bomb could be detonated many miles above America. Its effects would propagate outwards. The resultant electromagnetic pulse would break the electric grid including far more than just 9 EHV transformers.
A congressional committee formed of America’s brightest scientists, engineers, and industry experts, studied the problem for over a decade. They confirmed that the threat to our grid from a nuclear EMP is real.
Trump recently signed an executive order to harden the grid to protect against these attacks. In a best case scenario, this will take years to complete, and that is assuming the DHS does not thwart Trump.