John Brennan:

Well, I think it certainly didn't result in North Korea not acquiring a nuclear capability. Looking back over the last 20 years, I think successive administrations have tried their best to prevent North Korea from acquiring that type of capability.

It was a very long march that the North Koreans were on. And now they do have a nuclear weapons capability. And so I think it's appropriate that the Trump administration deal with this directly.

But this is a very difficult challenge. It has been a challenge for the last two decades. There has not been a military solution at all to this challenge because North Korea, not just because of its nuclear capability and ballistic missile capability, but it has so much conventional artillery that is within range of Seoul, the most densely populated city in the world, that even if we were able to take out all of its nuclear and ballistic missile capability, they could rain hell down on the people of Seoul and kill hundreds of thousands of people.

And let's not forget, we have about 200,000 American citizens in South Korea and 30,000 U.S. troops. So, there would be a lot of people who would be killed by North Korean artillery.