WASHINGTON — As Jerome H. Powell, the Federal Reserve chair, rang in 2020 in Florida, where he was celebrating his son’s wedding, his work life seemed to be entering a period of relative calm. President Trump’s public attacks on the central bank had eased up after 18 months of steady criticism, and the trade war with China seemed to be cooling, brightening the outlook for markets and the economy.Yet the earliest signs of a new — and far more dangerous — crisis were surfacing some 8,000 miles away. The novel coronavirus had been detected in Wuhan, China. Mr. Powell and his colleagues were …
