In December 2022, early into what he now describes as his political journey, Senator Chris Murphy of Connecticut gave a speech warning his fellow Democrats that they were ignoring a crisis staring them in the face. For over a year, President Biden and his allies had been promoting data showing an economic miracle, as friendly pundits described it — a record-setting stock market, low unemployment and G.D.P. growth outpacing that of almost every other Western nation. But very few voters believed the story those metrics were telling. In poll after poll, they expressed a bleak view of the economy —...