I think it's appropriate to pursue a ballistic missile defence capability. That capability is far from mature at the moment. Point defence is reasonably mature and realistic, but the problem of area defence is much more.... There you've got an expert community that is very skeptical of the defence ever being able to overwhelm offence, and that is if any country that has a sophisticated enough capacity to create ICBMs is going to have the capacity to build decoys into them and ways of circumventing missile defence.
So there is a very big job of pursuing a capability. I think where it's going wrong at the moment is the early deployment of a system that has a questionable capability but proves to be politically destabilizing in the Euro-Atlantic region.
I think the way forward is to move together cooperatively with Russia, pool resources, because we have a common interest there, and try to develop a genuine capacity, and also for mid-course interception. By the way, it's the capacity that could also have relevance as numbers of nuclear weapons get way low as protection against breakout and that sort of thing.
So BMD needs to be cooperative to be effective.