This week, the normally dour Federal Reserve chairman Jerome Powell started to sound kind of — could it be? — upbeat. The U.S. economy has made “a lot of progress” against rising prices, he said, after a crucial measure of inflation fell to 2.6 percent in May. (For those underwhelmed by this quote, it’s all relative; “a lot of progress” is as close to a rapturous statement as you could get from a Fed chair.) The upshot here is that with the inflation rate falling...