By fulfilling his campaign pledge to let the Argentinian peso trade freely, President Mauricio Macri did Brazil a nice neighborly favor. The real had been the worst-performing major emerging-market currency for months. Now that distinction belongs to the peso.
The peso fell against the U.S. dollar as soon as it started trading Thursday. As of mid-morning in New York, it was down 39 percent this year, compared with 32 percent for the real.