One comment, he talks about the substations like this is a small thing and asks what would happen if they blew up the Hoover dam. First of all, it would be incredibly difficult task to blow up the Hoover dam, probably way beyond the capability of people with guns and power tools.
Second if you can bring down the entire electric grid of the US then think of the issues. All refrigerations stops working so food will begin to rot in a couple of days. Also, all pumps stop working so people run out of water in a couple of days, gas stations stop working as well. All the transportation grinds to a halt which means the cities are out of food in a day or two. People don't have heat. Emergency vehicles stop working. Fires would not be able to be put out. Hospitals shut down. Phones all go dead in a couple of days.
This is huge, it isn't small. Second, you only need 10? You would think they have 1,000 operatives at least. If 5 million have crossed the border in the last 18 months then it is a small thing if 10,000 were operatives. Imagine the power has been off for three days, cop cars are out of fuel. It would be a simple thing to then sabotage so many other things. It would be scary to try and bring down a transmission substation with bolt cutters and an axe when the power is up, but easy when the power is down. Shoot up ten and then 100 others could be taken down with an axe and bolt cutters. So even when you try to get the power back up it keeps crashing.
If trucks can't run you will have massive supply chain issues in a week. You will also have bedlam in these cities with fire department and police departments being overwhelmed.