THE ROW over Mike Waltz’s security slip-up rages on. On March 11th America’s national security adviser accidentally added Jeffrey Goldberg, the editor-in-chief of the Atlantic, a magazine, to a group chat on Signal, an encrypted messaging app. Days later Mr Waltz and a succession of American officials including J.D. Vance, the vice-president, Pete Hegseth, the secretary of defence, Tulsi Gabbard, the director of national intelligence, and John Ratcliffe, the director of the CIA, used the group to discuss air strikes on Yemen. How serious a breach was this?