What Is the Terrorist Threat?

The Bush Administration keeps referring to the danger of "terrorism" to the American people as justification for the war on Iraq, NSA authorization, etc. The Administration continually points out that Al-Qaeda, for instance, wants to do us harm, to nuke us, or spread germs about, and kill many thousands of "Americans". Aside from the fact that such a feat is almost impossible to accomplish, even with the most well designed weapons, bringing in such weapons into the U.S. is very difficult; even as wide-open as our borders are, and plane cockpits are locked now. How many terrorists are there that could potentially "attack" the U.S., and realistically, with what? How about some specifics about numbers and methods to back up Administration claims?
The President makes a big deal about how "he" is protecting the American people, all the while he does all he can to prevent the shutting off of the stream of illegal aliens entering this country, many of whom end up "terrorizing" whole communities of Americans, fill our prisons, and cost us billions of dollars in medical bills and other governmental services. Some "protecting" of the American people!