The underlying reason that the United States has extended protection to South Korea really has nothing to do with Korea. It's all about showing the Japanese that the US is serious about protecting Japan in the Asian Pacific theater. The thinking goes that if we had allowed Kim to take North Korea in the 1950s, Japan would have had no choice but to militarize. The Japanese-American relationship has for some time been seen as the most important bilateral relationship in the world. This relationship, which includes the US defense umbrella, allows Japan to observe its constitution (which prohibits militarization) and to promote trade between the US and Japan. The thinking goes that if Japan becomes militarized (out of a lack of steadfastness by the United States) it could lead to massive conflicts in the region (i.e., with China) which would threaten US dominance in the region and which would disrupt global trade. I do not see how rattling the sabers with North Korea advances this longstanding bipartisan strategy of protecting the relationship between Japan and the US. If we turn up the heat too high in the region, Japan may feel compelled to abandon its constitution and take up arms. This in turn would set the Chinese off. This is a situation that requires consistent pressure and skilled diplomacy. Not hystrionics. Unfortunately, we have Trump in the White House, surrounded in large part by a bunch of neophytes.