Here's my thoughts on the analysis from Friday... Let me preface by saying that I believe the main threat to America is the lone wolf, a legal resident or immigrant, likely an American citizen converted to radicalized Islam or other extreme belief in prison or on the street. Just because someone is not a card carrying member of al-Queda or hasn't been to Yemen for terrorism training, doesn't make them any less of a threat. Perhaps they are more of a threat simply because they are overlooked. Google the term "sudden jihad syndrome" for a huge number of examples.
Biochemical Attacks - Reports that al-Queda of the Arabian Peninsula is seeking castor beans to make ricin... I don't see this as a major concern. Ricin is terribly lethal, but it's fairly easy to make, and castor beans are easy to get... I think that if it were a true threat, we'd already be experiencing it. I'm sure there are other biochemical threats, but there are easier and cheaper methods out there.
Radiological Bombs - the so-called "dirty bomb." Again, I don't think it is much of a threat. It would be fairly easy for them to get the radioactive materials, so why haven't they done it? It would cause extensive cleanup in the blast area of the bomb, but a car bomb or backpack bomb would cause the same amount of immediate destruction and mayhem, just not the long term residual problems.
Backpack Bombs in Shopping Malls - This is a real threat. A "lone wolf" can easily make a personal sized bomb that would take out him and a few bystanders. A small conspiracy group could plot for simultaneous attacks at locations around the country... just three or four would shut down our retail economy and then cause an over reaction like metal detectors at store entrances and M16 toting National Guardsmen at the supermarket. It's not just shopping malls. Imagine the reaction if four suicide bombers hit high schools in different parts of the country right at the bus loading section during dismissal, or what about if they mixed in with the crowds waiting to enter movie theaters or amusement parks before the gates open? Low cost, minimal planning and coordination (thus minimal opportunity for law enforcement infiltration), and impacting places that are generally seen as safe. This is probably the one that is the most worry for me, as far as the one that is most likely to actually happen.
Vehicle Bombs - These are less likely than personally carried explosives, just due to the quantities and skills needed to make them effective. Obviously, they have been used successfully in the US, but I think the odds of predeployment discovery are higher. Again, simultaneous attacks at various locations around the country would have the most long term impact.
Cyberterrorism - This is not something I know a great deal about, so I'll have to take the experts' words for it. I can say that the IT security guy at work once told me that we were getting thousands of intrusion attempts each day, most of them coming from Africa, China and Russia. The right attack on a banking system, defense system, or utility system could have catastrophic effects.
Small Aircraft Loaded with Explosives - This is another one that could easily happen; I don't even think the explosives are needed. Take a Cessna 152 or Piper Cub, two of the most prolific small planes around, and fly it into a crowd at a college football game, Tea Party rally, or a Hollywood awards ceremony. Do it at multiple football games at small colleges in the mid-West at the same time. It's not that difficult to earn a pilot's license, and then you can rent a 152 at nearly any municipal airport. As we recently saw at the Reno air races, just a plane crashing into a crowd can kill 10 or 15 people, no additional explosives needed. At an air race or air show, it's always in the back of the audience's mind that something like that could happen. At a small college football game, no one would think of such a thing... and the crowd would likely be denser with more injuries and death.
Look at the recent arrest of the guy who bought a radio controlled model plane and planned to load it with C4 and hit the Pentagon. His plan had almost no chance of actually causing any major damage. For the cost of his extremely high-tech model plane that he bought, he could have gotten his private pilot's license, rented a small plane, and flown it into football stadium at the Army-Navy game in Philadelphia, killing far more military leadership than he would have with his remote attack on the Pentagon.
Train Bombs - Again, we don't need to think too hard to come up with a realistic scenario here. Three killers with vest bombs, one on the NYC subway, one on the DC Metro, and one on the Chicago "El" train, all detonating at about the same time on a morning commute. Maybe a couple weeks later, two more who were inspired by the attack hit the San Francisco BART. Might only be a half dozen killed in each attack, but what would that do to the nation's economy if people in those cities wouldn't or couldn't go to work for a few weeks, or the capacity of those systems crashed because of the perceived need for searching all passengers and bags.
Energy Assets - Right outside of Washington D.C., along the I-395 inner loop, is a farm of oil tanks, each of which probably holds a couple million gallons of gasoline or fuel oil. The same tank farms are located along interstates outside of many major cities. A car pulls of to the shoulder at 2 or 3 o'clock in the morning, a couple of guys get out with RPGs
The other four risks mentioned in the article are not real specific, and are more organizational and planning oriented. Things not mentioned that have a history of being done in the US include plowing a car into a crowd on purpose (done at the University of North Carolina and on the Dulles (Va.) Airport connector road); mass killings in malls (Salt Lake City); poisoning salad bars (Antelope, Oregon); seemingly random "assassinations" on the street (fictionalized in "Unintended Consequences" and in the racist screed, "Hunter" - possibly happening for real against transvestites in DC right now). Of course, who can forget the DC snipers? A handful of random shootings shut down Maryland, Virginia and DC for nearly a month. Those two chowderheads probably would have gotten away with it had they not started leaving letters and making phone calls. On a side note, the priest that they called that ultimately lead to their arrests, was Father Sullivan of Ashland, Va. He's passed away now, but he married my wife and me.