A good thing to do in any case...
July 4th might be a very dangerous time in America!
It might be, but somehow I don't think so. I despise the terrorists and their supporters as much as anyone, but that doesn't mean I don't think them to be clever. They are. And when does a clever terrorist strike? When the target isn't expecting it.
Right now, we're all jittery. We're getting danger reports of various hue about nearly every aspect of our lives...subways, shopping malls, ships, small planes, bridges, dams, and what-have-you. I have a nasty suspicion that we're being fed a bunch of fake stories that will consume our time, effort, and attention. And in the meantime, the terrorists are planning something nasty.
And just what will that nasty surprise be? That's the big question, after all. We can't know the answer, but it seems likely that we can determine the general pattern from the 911 incident. First, they won't spend much money on it - they'll try to use our own stuff against us. It will probably target civilians. It will probably be simple...brutal, yes, but fundamentally simple. The cells will probably be small (5 or fewer) and only one or two of the terrorists will know the whole story.
For this reason, I'm not too worried about a radiological weapon, or (for that matter) even a biological one. Both violate the simplicity principle. I wouldn't expect an airplane attack again, because we're looking for that.
No, I think that I would worry more about an ancient tanker (financed with loans from a US bank, perhaps. Or leased from a US company) loaded down with ANFO coming into port...especially a port with lots of chemical plants, refineries, or a nuclear power plant. I think if I were connected with Homeland Security, I'd stay up late nights worrying about that one.
For this to be feasible you'd need a deepwater port with dense on-shore infrastructure. Most nuclear plants are near bodies of water but the depth is pretty shallow, so you perhaps couldn't float something like this up very close.
On the other hand, there may be other things out there of a much softer variety. One practical, real-world application of Homeland Security resources would be routine interdiction of port and river traffic near these areas. For example, the Bayway refinery in NJ, or some of those plants along the Houston ship channel...?