Taking down the power grid, even if only for a few days, would be much more devastating than even the economic blow to the US as a nation which occurred subsequent to 9/11.
Then, most of the communications nationwide was still up, and people still had access to money and most forms of ground transportation. New York City was heavily impacted, but was back up and running almost within hours after the dust had begun to settle, as much of the infrastructure outside a few blocks within Manhattan was still largely intact, if vastly overstressed at that point.
Harden and decentralize the power grid. This is both economically feasible and technologically available.
The nationwide interlocking grid was “efficient”, but it was and still is highly vulnerable, as knocking out just one major node causes ripples up and down the grid which sets up a domino pattern - as the separate parts of the grid go offline, the surge starts tripping out the next part of the grid and the next.
The next part of the strategy is to set up much smaller “cells” only tangentially connected to a larger grid, so these cells can respond by cutting out before the surge coming down the grid causes a local overload.
Then, as originating power generation within each of these “cells”, build a sufficient number of thorium-fueled Molten Salt nuclear power plants, which DO NOT have the inherent danger of uranium-powered light-water reactors, both from runaway operation of the plant causing meltdown, and the resulting spread of radioactive contamination. This means these plants may be built near or within the concentrated power consumption centers, WITHOUT the need for long-distance high-voltage lines and greater interdependence on the grid.
We COULD do some or all of these things.
Or we could just go ahead and nuke most of the power centers throughout the Middle East.
That second option would certainly be the quickest to implement and would regain the respect and fear of America that enemies no longer have.
Actually I think the second option is the better option now. We have let things deteriorate too far for the time consuming first option.
They will probably seize control of some part of the grid then as the rest of the grid tries to compensate and reroute power to the affected area the area under their control will be used to create chaos in the rest of the uncontrolled grid and the grid will end up frying itself.