The Department of Homeland Security (DHS) is still investigating a recent incident in which a large pipe bomb was found floating in Lake Pontchartrain, north of New Orleans. The device was examined, it was definitely a floating bomb, and was detonated while still on the water. While not a large explosive device, it reminded everyone at DHS that a major terrorist threat is the destruction of one of the railroad bridges over the Mississippi river. These bridges carry a major amount of freight traffic, and the loss of even one of them (if only for a few weeks, while being repaired) would have a noticeable effect on the economy. Al Qaeda knows about this, thus counter-terrorism officials are trying to found out who made the Lake Pontchartrain bomb. That's because this device had all the hallmarks of a test, for a larger bomb capable of dropping one of the nearby Mississippi river bridges.
Odd that he doesn't mention the other obvious job for a bomb like that: breaching the dikes. If the stories from New York have any validity, Al Qaeda (and/or sympathisers) were very impressed by the damage that followed Katrina. The story was they were looking for a method to flood New York, but that's very hard to do. To flood New Orleans again, however, would be (relatively) easy, provide great pictures for the world media, embarass the US government, and harm the economy of one of America's most impoprtant transit points. Is DHS really ignoring this, or do they not want to mention it?