"I think the terrorists who have done this obviously want to create the maximum impact," Clark says. "They've done it carefully enough to suggest that this isn't the end of the story."
He is not alone in this speculation. Jeff Stein, editor of Congressional Quarterly's Homeland Security Division, tells co-anchor Harry Smith, "Traditional terrorist doctrine, if you will, would flush people out of the subways and buildings, then set off another attack to injure the first responders that came to the site. So it could be a lot worse."
Clark notes, "The locations at the moment look as if they're relatively carefully planned." The series of believed-to-be terrorist explosions targeted London's subway system and a double-decker bus during the morning rush hour.
Clark says, "At the moment, central London is more or less closed down in the sense that there's no public transport, that telephone systems are a bit intermittent at the moment. And everyone in central London is being told to stay put and there will be some announcements later on about what public transport there is to get people home."
Stein says Americans should be thankful. "You can see what happened in London has paralyzed the transit system and shut it down. That's not just ordinary people not being able to get around - that includes security officials. The same thing would happen in Washington. If you paralyze the metro system, a lot of people would have trouble getting to work, including homeland security officials. So that's what this kind of bomb does. It sows confusion; it paralyzes a transit system. It doesn't do that much damage, the deaths of ordinary citizens, but not like the World Trade Center."
And yet, Clark notes, there is no sense of panic in London. "People are wandering around, talking about what they think all the impact will be," he says.
Stein says, "The British have a lot of experience dealing with this kind of terrorism. They have experience, 30 years with terrorists going back to a lot of the Palestinian groups. So they're well practiced at this - much better than we are. We are late to the game."
Referring to the attacks, Stein points out, "We all have to recognize that security on the rails and buses and subways is the last line of defense. The first line is very good intelligence. That's very hard to get, especially in European cities where there are large Muslim populations in which the terrorists can swim. So this is not to cast any aspersion on the millions, and millions of Muslims that do not support al Qaeda, of course. But they can swim in these communities;- whereas they would stand out in other cities."
As for possible attacks on American soil, Stein says Washington, D.C., has been warned.
He says, ", the operations chief of al Qaeda who was captured last year, reportedly said that al Qaeda was planning attacks on the D.C. Metro system. Now, maybe they're going to tell us that we've intercepted some of those plots; however, I have a feeling we would have known about it because intelligence officials are eager to show they're on top of their game right now. Rand Corporation put a study out last year, saying that rail systems and subway systems are a priority target. These are lower level targets than the World Trade Center, you know, or big spectaculars like that."