I would just say two things.
One is—and I defer to my colleagues in terms of more specialized knowledge—that the developments in this conversation on U.S.-Korea so far underscore the point I made earlier about the importance of preparation. The example I would give is the language around “denuclearization of the peninsula”. That term means something very different to Kim Jong-un than it does to Donald Trump.
It is important, in preparing for senior-level meetings, to have staff-work that goes into clarifying terms, so that we're talking about the same thing. Then we can make decisions on purposeful ambiguity and all the rest of it. Therefore, the lack of staff-work on that could lead to a dangerous possibility of a breakdown in the meeting, because what Kim Jong-un thinks is denuclearization of the peninsula involves at least the withdrawal of U.S. nuclear capacity, whereas the U.S. position has been thinking about it purely in terms of North Korea. That would be, as Charles indicates, quite dangerous. It's important, then, when we have these terms, that we use the local meaning, that we understand that meaning, and that we understand that it's not our meaning.
The second point is that the North Korea matter has to be seen in the context of Iran. I think President Trump's comments just this morning on Iran are probably giving people in Korea pause, in terms of how reliable a partner they think the United States will be. We could talk about Korea, but the behaviour of the United States toward Iran is one that has given pause.
I think those are two factors that should be borne in mind, but I defer to my colleagues.