Why is this such an important issue? Because, if you believe, as Selva and others apparently do, that North Korea cannot yet attack the homeland with a nuclear weapon, it follows that the United States can take preemptive military action against North Korea without risking a retaliatory nuclear strike by Pyongyang. You can take such action without putting the United States at risk.
However, if you believe, as I do, that North Korea might be capable of striking us today, it follows that a preemptive U.S. military strike against Pyongyang could bring about the very thing that we are working to avoid — the nuclear annihilation of a U.S. city and the deaths of millions of Americans. If this darkest of scenarios were to play out, the assumption and assessment that North Korea cannot yet threaten us would be a strategic mistake of historic proportions.