This is one of those situations where one reason no one has done anything about it is because there are no good options. We have 35k troops in SK as a tripwire to deter NK. I question the morality of that. SK has three times the North's population and a massive economy. It does seem to me they are perfectly capable of defending themselves if it comes to that. We gave them 65 years to get ready to deal with the North. Enough is enough. Why should we have our troops there as sitting ducks in an indefensible posture?
Now they are carping about paying for the THAAD system Trump put there. Their new administration does not even want it. So they would like our troops, but no missile defense for them. OK, that doesn't work for me.
The first step is to pull our troops out. The next step is to tell China that SK is free to develop nukes, as is Japan. Or, if they find that prospect unappealing, they can enact regime change in NK.
A massive preemptive attack on NK is another option. SK is dead set against that. Their objections are understandable, but when we are talking about preventing a possible attack on our own country, SK does not have a veto over our actions. It is only a matter of time before NK has the ability to cause massive damage to our country. No doubt we will wait until that point to do something.
Attacking NK would be a clear act of war that would require a declaration of war by the congress. Perhaps such a vote would focus their minds.