Attorney General William Barr got attention when he told Congress he’d examine the origins and predicate for the Federal Bureau of Investigation’s counterintelligence probe of the Trump campaign. He surely set off alarms in certain precincts when he added: “I am not talking about the FBI necessarily, but intelligence agencies more broadly.”

The need for thoroughgoing reform of America’s intelligence services and processes is evident. It wouldn’t be the first such effort. After World War II, Congress established the Central...