June’s inflation index jumped 5.4% from a year ago, the highest reading since August 2008. The experts were surprised. Clearly, Federal Reserve watchers never bothered to consult Milton Friedman. Lost is a core Friedman dictum: “Inflation is always and everywhere a monetary phenomenon.”

In his Feb. 23 testimony to Congress, Fed Chairman Jerome Powell said that the growth in the money supply, specifically M2, “doesn’t really have important implications.” The experts, the press and the bond vigilantes were as quick to unlearn monetarism, if they ever had learned it, as Mr. Powell. Reporting about U.S. inflation rarely contains the words “money supply.” We are repeatedly told that the most recent upticks in inflation are anomalous and “transitory.”

Wrong. The inflation upticks aren’t temporary and were predictable, driven by an extraordinary explosion in the money supply. Since March 2020, the M2 has been growing at an average annualized rate of 23.9%—the fastest since World War II. There is so much money out there that banks don’t know what to do with it. Via reverse repurchase agreements, banks and money-market funds are lending money to the Fed to the tune of $860 billion. That’s unprecedented.