Would America dare to bring down a Chinese bank?

If any politician has the demeanour to ease tensions with Beijing, it is Janet Yellen. America’s treasury secretary comes across as a twinkly eyed professor, rather than a foreign-policy hawk. Sure enough, she used a recent trip to China, which ended on April 9th, to praise the “stronger footing” that Sino-American relations are now on compared with a year ago. Ms Yellen was not merely there to extend an olive branch, however. She also carried a warning for China’s banks: those that help “channel military or dual-use goods to Russia’s defence-industrial base expose themselves to the risk of US sanctions”.