Attorney General William Barr on Monday announced the Justice Department’s first policy change in response to the FBI’s mucking around in the 2016 election. Henceforth, both an AG and the FBI director must sign off on any proposed counterintelligence investigation into a presidential campaign. Three cheers for future accountability.

Amazingly, no such basic rule has existed. FBI policy allowed even sensitive investigations to proceed with little more than a review by an FBI lawyer and approval from a supervisor. Justice Department...