Arguably the most dangerous threat to US existence is the detonation of a nuclear device above the North America.

A congressional committee, in 2008, concluded:

Quote:Rogue nations such as North Korea (and possibly Iran) will soon match Russia and China and have the primary ingredients for an EMP attack: simple ballistic missiles such as Scuds that could be launched from a freighter near our shores; space-launch vehicles able to loft low-earth-orbit satellites; and simple low-yield nuclear weapons that can generate gamma rays and fireballs.

The damage? They estimated:

Quote:that within 12 months of a nationwide blackout, up to 90% of the U.S. population could possibly perish from starvation, disease and societal breakdown.

The cost t0 protect against an attack:

Quote:..Surge arrestors, faraday cages and other devices that prevent EMP from damaging electronics, as well micro-grids that are inherently less susceptible to EMP....would be about $2 billion...

Although $2 billion sounds a bit low to protect the entire system, would even $20 billion be too much.

EMP Threat

This is something that should have been done years ago not just due to EMP but also due to solar storms.

This is actually a really big potential problem that has a few relatively cheap solutions. The nation is currently divided into 3 power grids (east, west, Texas) but it really needs to be divided into much more. That plus the suggestions in the article should be implemented ASAP.