By ignoring the role of politics, economists often get it wrong. How many trade specialists were prepared for the recent breakdown of the Doha trade talks, despite the obvious gains to be had on all sides from a new round of liberalisation?
The answer is almost everyone (Jagdish Bhagwati’s strategic optimism notwithstanding). Trade specialists are (sadly) well aware of the political constraints that shape trade policy.
Trade Diversion 
Well, this IPE guy disagrees with Cohen. “…obvious gains to be had on all sides from a new round of liberalisation?” I’ll bet the globalization sceptics, Dani Rodrik and a host of others would beg to differ.