65 years after the 1953 armistice that stopped the open fighting of the Korean War, the nations involved still haven't replaced it with a permanent peace treaty. This means that the Korean War is still technically ongoing, 68 years later. That's apparently where the US intends for it to stay.
While North and South Korea have discussed deals to end the war, and the US nominally has given its imprimatur to the idea, US officials say that there is little interest in the Trump Administration to actually do this, with some seeing it as undermining their leverage against North Korea on denuclearization.
This would be a complicated matter this time, unlike the decades of previous US resistance to making peace with North Korea. That's because now, South Korea is also on board for such a deal. In trying to delay such an important milestone, the US may be seen as obstructing diplomacy in general.