If we lose 1/3 of our refineries, we lose about ~1/3 of our gasoline. The prices shoot up to ludicrous highs, but it's still there. We might have to make an expensive deal with Saudi Arabia to fill the void, but at least that's an option.
If we lose, according to FERC (Federal Energy Regulatory Commission)... nine... of our 55,000 substations; the entire nation could lose power in almost all areas. Maybe our situation has improved since 2014, I definitely hope so, but think about this:
33% causing ~33% damage, or 0.016% causing ~90% damage. Which one is preferable?
Here's a genius idea if you're Russia. Maybe things have improved and are 10x better. In that case, knocking out 0.16% of our substations, 90 in total, in strategic locations should do the trick. Combine that with rail sabotage so the parts to fix them don't arrive, and then you've done it. Just smuggle about 500 soldiers among the 2.2 million illegal border crossings every year, and that'd be enough to assign a team of 5 to each task.