2. Once escalation starts, it can be difficult to control
When dealing with a new nuclear power, it is important to know that once escalation starts, it can be extremely difficult to control. A deliberate and limited US response is still likely to result in extreme escalating actions by North Korean adversary forces. These could include the early use of nuclear weapons.
There could be a mix of reasons why controlling escalation may be difficult in real crises. One might be the efficiency with which the US has overthrown the governments of its adversaries in recent years. These operations almost always began with an intensive air campaign to cripple strategic targets, such as leadership facilities and national-level command-and-control communication centers.
These types of attacks, which have become mainstays of the US military repertoire, could be perceived by adversary leaders as threats to their hold on power, and therefore could prompt escalation.