Iowa lawmakers last week continued their defense of the Renewable Fuels Standard (RFS) against a full-scale as­­sault by the oil industry and oth­­ers.

Iowa Sen. Charles Grass­ley pressed the Environmental Protection Agency (EPA) to in­­crease the transparency of the market for Renewable Identification Numbers or RINs. He expressed concerns that the RIN market is being manipulated by Wall Street banks and other financial institutions that could undermine the effectiveness of the RFS.

The RIN trading...