The return of the renminbi rant

China's currency, the renminbi, has been weakening in recent months, resurrecting familiar charges of manipulation, competitive devaluation, and beggar-thy-neighbor mercantilism. In mid-April, the US Treasury expressed "particularly serious concerns" over this development, underscoring what has long been one of the most contentious economic-policy issues between the United States and China.

This is a timeworn debate - politically inspired and grounded in bad economics - that does a serious disservice to both sides by diverting attention from far more important issues affecting the US-China economic relationship. Taken to its extreme, America's accusations risk pushing the world's two largest economies down the slippery slope of trade frictions, protectionism, or something even worse.

First, the facts: Since hitting its high watermark on January 14, the renminbi has depreciated by 3.4 percent relative to the US dollar through April 25. This follows a cumulative appreciation of 37 percent since July 21, 2005, when China dropped its dollar peg and shifted its currency regime to a so-called "managed float." Relative to where it started nearly nine years ago, the renminbi is still up 32.5 percent.