International travel by world leaders is mainly about making symbolic gestures. Nobody expects President Obama to come back from China with major new agreements, on economic policy or anything else.

Paul Krugman

But let’s hope that when the cameras aren’t rolling Mr. Obama and his hosts engage in some frank talk about currency policy. For the problem of international trade imbalances is about to get substantially worse. And there’s a potentially ugly confrontation looming unless China mends its ways.

Some background: Most of the world’s major currencies “float” against one another. That is, their relative values move up or down depending on market forces. That doesn’t necessarily mean that governments pursue...