In the final months of the Obama presidency, U.S. officials are scrambling to salvage the Trans-Pacific Partnership trade deal, which is facing opposition in Congress. Negotiations over a U.S.-EU deal—the Trans-Atlantic Trade and Investment Partnership, or TTIP—are meeting equally daunting challenges. The U.S.-EU commercial relationship is full of issues, such as agricultural trade, which have proved intractable for decades, along with newer disputes such as post-Edward Snowden standards for data-privacy protection.

Discouraged...