I am concerned about the PR aspects of the EMP attack risk communication over the last couple years. Awareness of the EMP risk has spread much faster among the right than any other portion of the political spectrum. This is already making it unfashionable among the educated left.
Given the year (2010), I currently think that EMP attack is the second greatest risk we face, right behind a genetically engineered superplague. A small EMP-optimized nuke launched from a container ship in the Gulf of Mexico could take out the power grid of the entire continental United States. The same thing could be done anywhere, like Europe or Japan.
The facts are available from the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack. No one cares except the Fox News crowd. It wasn't like this only a few years ago: EMP attack was primarily a topic limited to analysts and sci-fi TV show writers. Obama seems concerned about nukes in general (which presumably includes the EMP risk that emanates from them), but not many on the left share his concern. People are too busy worrying about global warming. The aging Henry Kissinger is not a good spokesman for the nuclear security movement.
If an EMP attack came, cars and trucks would just stop. Factories, controlled by computers, would stop. Molten steel on the assembly line would cool and solidify in place due to failure of the heating elements. The vast majority of tractors, combines, and other heavy machinery would become useless. Transformers and other electrical elements, large and small, would be fried. The largest transformers have to be ordered from China and are generally ordered with a year of lead time.
An effective EMP attack on the US would cause tens of trillions of dollars of damage. Cities would run out of food in a few days. The US grain stockpile only has about a million bushels of wheat. Wheat is the only common grain with enough nutrients to sustain someone on an all-grain diet. A bushel is only 60 pounds, and someone needs about a pound of wheat a day to avoid hunger pangs. Ideally two pounds if you are doing manual labor. 60 million man-days of food is not a lot. The population of the United States is 300 million. That means our grain stockpiles are enough food for everyone to eat a fifth of a pound and then they're gone.
The long-term prognosis will depend on how hard it will be to get crucial electronics for trucks and tractors in. If security collapses a few weeks after an EMP attack, foreign companies may be reluctant to do business here.
For a few tens of billions of dollars, we (the US) could shield our most important infrastructure from EMP attack. Our power grid is so naked and unprotected right now, we are practically asking to be nuked.