Where to begin on this topic? Let me start with several "to be sure" statements and then the clearest formulation of the issue I can manage.
The real counterpart to Smoot-Hawley [after this crash] would be Chinese protectionism --or rather, any effort by China to defend its huge trade surpluses, as the U.S. once did. China's government is unlikely to rely on outright Smoot-Hawley-style tariffs. Instead it could increase subsidies to exporters; it could try to push the RMB's value back down, after three years of letting the currency rise; it could encourage manufacturers to restrain wages; it could impose indirect barriers to imports, as with its recent pressure on China's airlines to cancel outstanding orders for Boeing and Airbus airplanes. By early this year , China's government was in fact doing every one of these things... This is an economic problem for other countries. But it could be an even more serious political provocation, if China is seen as forcing its share of unemployment problems onto everyone else.
That's where we are now. China's government has helped its own economy recover by holding the RMB's value steady against the dollar rather than letting it rise. But in doing so it has made recovery harder in the United States and -- more dramatically -- Europe and Japan, since the RMB has joined the dollar in falling in value against those currencies. This is not a matter of "manipulating" a currency, and I wish American politicians would stop using that term. But it is destructive to overall world prospects for recovery, because it is hurting everyone else. You don't need any advanced trade theory or specific industrial analysis to know this. It is necessarily true as a matter of basic math: a depressed world economy needs more demand, and an artificially low national currency means artificially restricted demand from that country.