On 13 March, Donald Trump’s national security adviser, Michael Waltz, who was the policy director for two secretaries of defense and was a member of the House intelligence committee, sent a message on the commercial Signal app: “Team – establishing a principles group for coordination on Houthis, particularly for over the next 72 hours.” “The Houthis PC small group” would oversee a US air attack on the Houthis in Yemen. Despite Waltz’s extensive professional background, he misspelled “principals” as “principles” – perhaps an ordinary typo, but symptomatic of the shambles to come. Although the secretaries of defense, state and treasury,...