It's always easier to see the connections of those dots when you look back. We know that it was Umar Farouk Abdulmutallab who chose to set himself on fire in an attempt to bring down an airliner. So we can trace his path back.
Likewise, we can trace Nidal Hasan's path back before he went on his shooting spree at Fort Hood.
But it's harder to do that prospectively. There are half-a-million names on the broadest US terrorist list. At any given time, relatives may be complaining about some of those people, calling them terrorists or suspect in some other way. As we look back, the connection between his father's warning and Abdulmutallab's actions seem clear. But as one of a multitude, not so much.
Here's another problem in sorting things out prospectively: how do we know who will live and who will die with any given medical procedure? The answer is that we don't. As Peter Orzag is quoted in that piece,
One of them costs twice as much as the other, and I can tell you that we have no idea what we’re getting in exchange for the extra $25,000 a year...Now that sounds like a condemnation of the more expensive care, and maybe it is, but I choose to take it as a statement of what we don't know.
It's useful to look back, but the value of retrospective analysis is to find things we didn't know, not to assess blame. Of course, we have Republicans spewing blame around like bullets from a Kalashnikov, and it's been the fashion for so long that the media have a hard time framing their stories any other way than pointing fingers.
Here's an interesting commonality between Abdulmutallab and Hasan: Both seem to have had the same guru in Yemen. And it might even be possible to figure out what went wrong in both their cases.
And once we know that, we might be able to craft workable preventions, or recognize that we can live with uncertainty.