This is from the U.S. statement at yesterday's DSB meeting, commenting on the Tuna 21.5 panel and Appellate Body reports:
Panels and the Appellate Body should not make their conception of the “perfect” measure the enemy of all the possible good ones. In pursuing legitimate objectives, Members should not be held to the impossible standard of designing and applying a measure that corresponds exactly to the one that a panel or the Appellate Body would have designed to achieve the legitimate objective at issue.
Do WTO obligations ever require perfect measures? What about the requirements that SPS measures be science-based? Or that TBT measures not be more trade-restrictive than necessary? And now the AB has applied a high standard of regulatory competence under the "stems exclusively from a legitimate regulatory distinction" element of less favorable treatment.