A good point. Hopefully he's attacking the problem at the source for now, then will get our borders protected later.
As I told my son yesterday, the cost of protection FROM WMD would be extremely expensive. The cost of preventing CREATION of WMD could be as little as the cost of ONE BULLET.
I don't think you can prevent people from creating (and therefore selling, and therefore obtaining WMD). You would have to "unteach" a technology, like teaching them to forget algebra or geography. Like shoving toothpaste back into the tube.
The long-term solution is two-fold: First, a re-evaluation of our foreign policy, and a policy to get us the hell out of places we aren't wanted, which is just about everywhere but good ol' terra firma USA. Let the rest of the world learn to diaper itself.
Second, make it very clear, that any terrorist action will be met swiftly, brutally and finally with annihilation, and be prepared to back it up. Even nukes if necessary.
But the second is meaningless without the first.