Pull back from Korea as soon as the situation with the North is resolved.
Define "resolved".
Oh if I had a nickel for every time Alan asked for those devilish details!
Basically, "resolved" has to ultimately defined by Trump...and it may not occur until his second term...that is if the DeepState and their fellow domestic terrorists fail in their coup attempts.
We always knew the "devil was in the details" with any deal with North Korea, especially with any Kim dictator at hand, so perhaps the strategic "resolved" can be replaced with "contained" and the continued pressure to apply be our resolute tactic.
The facts are quite simple actually, they have nuclear capacity and arguably reliable delivery means that can unarguably cause great catastrophe. They also have a history of only protecting and caring most for the elite in their society and the caste nature of their concern leaves the great unwashed ignorant, dirty, cold and hungry. The key is to exploit the yearning of better for the lower castes and the appeal of more and better riches for the elite...if they dismantle current production of weapons grade material and delivery means and dismantle existing delivery means. I doubt they will ever fully relinquish their existing nuclear material, but if we can render it to a secure vault never to be opened it may be the best we can hope for, until such time as enough time has passed that changes the regime from within. It has to be a carrot and stick approach and no wavering with these guys, and so far the Trump Admin seems to be working it firmly. It's going to be dribs and drabs...and sadly it may only live so long as Trump does in the White House.
Anyway, back to the troops...to keep Kim & Co in their box and behaving as desired does not require troops on the peninsula, however their presence is a symbol, and I would keep that piece on the table until such time we got an equally dramatic matching move by the North. We would still have frequent port calls by the 7th fleet, we would still have basing rights if needed and still have the strategic means to reduce much of the North to ash should they go full-retard...troops and planes on the ground would not be necessary to keep them in check.
Basically, one phase at a time, and bag doggies get no treats. And it should work, the populace and its lesser castes may appear docile and much of that is due to state imposed ignorance and propaganda....but time is not on their side, history shows there is a limit to oppression, it is a matter of when not if. All we have to do is be committed to the strategy and see it through.