A couple of possibilities here.
First, perhaps this is a reality check that no amount of sanctions and diplomatic pressure is going to stop a regime so committed to the task. If we're not willing to make multiple, repeated military strikes, perhaps even put troops in-country, there may be no reasonable expectation of stopping NK.
Second, and perhaps more cause for concern, it may be that there is no point in trying to prevent NK from developing nuclear weapons, because they already have them? Consider, their first nuclear weapons test was back in 2006. They've performed a total of 6 to date. The last several apparently relatively sophisticated devices utilizing either a multi-stage design (claimed, but probably unlikely) or a boosted fission design. That is a long time and they've been putting a lot of effort into it.
Oh, and before you lib lurkers start blaming President Trump for this, 5 of the 6 tests occurred before he took office. That's right sports fans, NK's rapid development and advancement of capability came under bammy's watch. Imagine that. Now President Trump has to deal with the reality of NK very likely already having nuclear devices in a weaponized configuration. The only real question is, can they survive a missile flight and re-entry and still operate... Well, there's several other questions too but that's the big one.
That’s why we have Counter Force, the preemption of capacity.