North Korea appears to have tested a hydrogen (nuclear fusion) bomb, generating their largest blast to date.
**source: Norsar Website
Do they have a nuclear bomb that is small enough to fit atop a missile? Maybe. Do they have an ICBM that can reach the continental U.S.? Maybe. Do they have a ballistic missile that can reach U.S. territory at least somewhere? Yes. Can they cause extreme devastation even if they don't have a re-entry vehicle that can survive re-entry? Yes. (Look up electromagnetic pulse--or EMP--for more information on this.) Are they working to develop all of these capabilities as quickly as possible and faster than they ever have? Definitely.
Most important, would Kim Jong-un actually preemptively use a nuclear weapon against the U.S.? Probably not. Doing so would invite the complete destruction of the North Korean regime; maintaining this regime is Kim's highest priority.
That said, we cannot say for sure that Kim wouldn't either use a nuclear bomb pre-emptively or initiate hostilities to reunify the Korean peninsula and use his nuclear weapons as a deterrent to try to ensure that the U.S. wouldn't interfere. Assuming these things means assuming that Kim is a completely rational actor, that he is a well informed actor, that he receives sound advice (especially about the lack of capability of his own military relative to that of the U.S. military), that his perceptions of U.S. red lines are accurate, that his assessments of likely American responses are accurate, and much more. Can we be absolutely certain of all of these things? Unfortunately, no, we cannot be; the most we can is "probably."
Therein lies the real problem: Is "probably" enough assurance that the President can risk the lives of millions by doing essentially nothing?
At this point, we really have two options, one that would end North Korea's nuclear program (and probably its regime) and one that would allow them to develop a fully threatening nuclear weapons program. The former is, of course, military action. The latter is "everything else" (sanctions, diplomacy, and so on). At this point, the one thing we can say with confidence is that neither sanctions nor talks nor diplomacy nor anything else will stop Kim's nuclear ambitions; only military action can do that. In fact, nothing but military action is likely even to slow North Korea's progress toward a fully viable nuclear weapons program. Sanctions and talks have always been a means of kicking the can down the road. The problem is that eventually the road reaches a dead end, and you must make a real and lasting--and difficult--decision.
That really is where we are now. The time for a decision has arrived; it cannot be put off any longer. The President has threated "fire and fury." So far "fire and fury" has meant more talking, more threats, more tweeting, etc.--nothing of consequence and nothing that will actually change anything (and certainly nothing that anyone would recognize as either fire or fury). Now the security of the Korean peninsula isn't the only thing on the line: the President's credibility is as well.
We must now decide whether we can live with a North Korean regime that has deliverable nuclear weapons and that threatens to use them against us, which is an unprecedented combination. If we can live with this inevitable outcome, then we can continue pursuing talks, sanctions, and UN resolutions. North Korea will simply say "noted" and continue forward. (We must also consider the broader implications of de facto acquiescence to a North Korean nuclear weapons program. If we will allow them to have nuclear weapons, then why not Japan? South Korea? Iran? Saudi Arabia? What about the very viability of the nuclear non-proliferation framework? These too must be considered.)
If we cannot live with this arrangement, then there is only one option left to us: military action. The sooner this decision is made, the better. No decision is now a decision. That time has arrived.