Vietnam rightly worries about the harm U.S. tariffs will inflict on its success and even more bullish aspirations. The levies will slow an economy that's racked up impressive rates of growth. The past few months have also revealed a challenge of a different nature: A declining birth rate.

This is a country, often hailed as a development model, that has a lot on its plate. It should avoid going overboard on sweating demographics. That’s not an existential issue — yet. In some ways, the trend toward fewer births could even be called a victory. Trade, linked so intimately with the decades-old industrialization plan, is the more vital front. The setting of priorities is important, but they can travel on two tracks.

The government recently scrapped a long-standing rule that limited households to no more than two kids. Couples will now be allowed to welcome as many babies as they wish. At first glance, the shift looks dramatic and recalls China's panicked jettisoning of its iconic one-child policy a decade ago. All the more so because both nations have communist rulers, showed a penchant for central planning before discovering that markets can enrich and saw pint-sized families as a path to poverty elimination.