Very quickly, generally threats today are perceived in terms of capabilities that could pose a threat.
In the state world, these are capabilities in the absence of political intent, except for concerns about North Korea and, to a lesser degree, Iran. In the non-state world, they are also capability based. We imagine different ways terrorists.... We can identify terrorists who have said they are going to get us. Al-Qaeda and, more recently, ISIS are on that list. That's why we tend to focus more attention on them. Both of them, along with the planning and thinking and investments, are really a function of being able to identify a large set of capabilities that could threaten North America. That's great, but then what do we do?
In terms of the ballistic missile question, we know that North Korea has tested a long-range ICBM. Terrorists don't get ballistic missiles. We know they have tested nuclear devices. Can they reach North America? Can they target Canada? Will they target Canada? Those things remain to be seen. Iran is somewhat of a step down from North Korea in that. Should we be concerned about a potential North Korean bolt out of the blue? Possibly. Is it a major concern, a major threat to North America? The United States sees this a little differently from the way I do. I would say, for the time being, no.