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When the self-proclaimed "conscience of liberal America" and a one-time free trader to boot starts arguing for protectionism, you know that things have come to a pretty pass. But that's what's happened over the past week.

Paul Krugman, a Nobel Prize-winning economist, has taken to advocating a 25 per cent "surcharge" – he refuses to use the more descriptive term of "import tariff" – on goods from China as a way of bringing the Chinese leadership to heel over currency reform. So potentially dangerous and out of character is this idea that when I first read it, I assumed he was being ironic. But sometimes the cleverest of people can also be the most stupid, and he's now said it so often that you have to believe he's serious.