The third nuclear test conducted by North Korea on Feb. 12 was the latest in a long history of provocations. In many capitals, this event was noted with some alarm and then more or less pushed aside by other issues. Not so for denizens of the southern half of the Korean Peninsula. There, the North’s nuclear test was so threatening that it has moved onto center stage a once-fringe debate about whether South Korea should acquire nuclear weapons of its own. Washington and Beijing should take notice.