The Trump administration appears to have landed on a fallback strategy in the Iran war after military strikes and negotiations failed to deliver victory: threats of harsh economic sanctions. Treasury Secretary Scott Bessent has called them the “toughest sanctions in history,” which will “collapse this regime.” He’s even called it an “economic D-Day” for Iran, comparing it to the historic invasion of Nazi-occupied France during World War II. There’s just one problem: Making good on those tough words requires not just getting tough on Iran, but also getting tough on China, which is Tehran’s No. 1 trading partner. And Trump...