This is a very useful primer on interwar protectionism by the leading historian of US trade policy. (I had never heard of ‘Smoot Smites Smut’, which is worth the price of admission alone.) Although Doug could have usefully mentioned that the biggest costs of protectionism then were geopolitical, and those ended up being fairly catastrophic.
Economists sometimes assume that the right way to talk about protectionism is to moralize. I prefer analyzing the causes of protectionism: it may be a very bad idea, but sometimes, in democracies, it becomes inevitable. Doug, in a manner reminiscent of Adam Posen, argues that expansionary monetary policies in the US are a good way of keeping the protectionist wolf at bay there right now. The same logic applies to Europe as well.