US Treasury Secretary Janet Yellen committed a string of diplomatic faux pas during her visit to Beijing Saturday, bowing to her Chinese counterpart multiple times without reciprocation — a protocol error that critics flagged as a sign of American weakness. The Biden administration’s top economic official, on the second day of her four-day effort to mend fences with a major rival, bowed at least three times as she shook hands with Vice Premier He Lifeng, video shows — while He, Xi Jinping’s new economy czar, stood erect, backing away slightly to give the beaming Yellen more room to kowtow. “Never,...