With CNN interviewing people like Tom Clancy (no joke), there will be no shortage of people calling for Americans to trade in some more freedom in return for a promise of more security. Benjamin Franklin correctly said that the people who would make that trade would neither get nor deserve freedom or security (via adam or randomWalks from Indymedia).
In response, we should think carefully about our security. This is a horrible thing. But it doesn't happen often, and it won't. There are only so many things we can reasonably protect ourselves against (I've said this before in criticism of the Missle Defense Shield). These events should be reviewed and applicable lessons should be learned and acted out. However, I think it would be a mistake to violate personal liberties seeking justice for this action or seeking to prevent such and action in the future.