When Donald Trump warned Iran on April 7 that “a whole civilization will die tonight,” a European diplomat in Washington said his government wanted an urgent answer to a chilling question: Was the US president contemplating the use of a nuclear weapon?

Across Europe and Asia, the concern went beyond whether Trump’s apocalyptic threat was real or bluster. 

European governments immediately sought reassurance through a traditional channel: the US State Department. But according to the diplomat, officials there gave an unsettling response: They didn’t know what Trump meant or what actions his words might portend.

The previously unreported episode points to a historic breakdown in American diplomacy. At a moment when a uniquely unpredictable president is rattling markets and capitals with dramatic pronouncements, governments around the world are scrambling for clarity, only to discover that their usual points of contact – at US embassies or inside Washington – are missing, mute or out of the loop. At least half of America’s 195 ambassadorial posts worldwide are now vacant.

Our account of America’s diplomatic upheaval is based on interviews with more than 50 senior diplomats, White House officials and recently retired ambassadors, as well as dozens of foreign officials, diplomats and lawmakers across Europe and Asia.