“What I was told is that there was concern that the rug would be pulled out from underneath the State Department if they put out something publicly,” Yovanovitch said. Not even Pompeo, one of the president’s closest advisers, could do something as mundane as endorse a sitting ambassador for fear that Trump might humiliate and undermine him.

Yovanovitch’s account is hers alone, of course; some of the relevant State Department officials have testified, but transcripts of their depositions have not yet been released. But the ambassador is speaking under oath, and her account reflects a tendency that is already clear: The federal government is terrified of Donald Trump’s Twitter account.

Since taking office, the president has often struggled to enact his desired policies and actions, for a variety of reasons: a noncompliant Congress (under both Democratic and Republican leadership); his own short attention span or inattention to detail; and sometimes the best efforts of his own aides to stymie him. Where the ordinary policy process fails Trump, he sometimes turns to his Twitter account, and has often found it more effective than traditional channels.

The lack of support for Yovanovitch in March wasn’t the only example of the State Department’s terror about Trump’s tweets. A month later, Yovanovitch received a call from Washington at 1 a.m. Kiev time, telling her to be on the next plane back to the United States. She was told it was for her own “security” and “well-being.” Back in the capital, she met with then–Deputy Secretary John Sullivan.

“The deputy secretary said that, you know, he was sorry this was all happening, that the president had lost confidence, and I would need to depart my post,” she recalled. “I said, what have I done wrong? And he said, you’ve done nothing wrong. And he said that he had had to speak to ambassadors who had been recalled for cause before and this was not that.”

Then Sullivan explained why she’d been ordered home so abruptly: “The reason they pulled me back is that they were worried that if I wasn’t, you know, physically out of Ukraine, that there would be, you know, some sort of public … tweet or something else from the White House,” she said. “And so this was to make sure that I would be treated with as much respect as possible.” The State Department was terrified of the prospect of a presidential tweet and was scrambling to protect its own loyal officers from the president.

Twitter is often seen as Trump’s most effective tool for communicating with the general population, but as Yovanovitch’s account shows, it may be most effective at cowing bureaucrats and forcing them to comply with his wishes.

Read: There is no American ‘deep state’

Though the administration has been ever more, as Thomas Wright notes, overtaken by yes-men, Trump has often in the past found his aides unwilling to do things that they think are stupid, foolhardy, or self-destructive. Former White House Counsel Don McGahn refused to fire Special Counsel Robert Mueller, for Trump’s own good. The former economic adviser Gary Cohn delayed tariffs and even swiped a letter terminating a trade agreement from the president’s desk to prevent him from signing it. Former Defense Secretary James Mattis reportedly simply refused to do things Trump told him to do, from attempting to kill the Syrian dictator Bashar al-Assad to punishing Amazon for harsh coverage in The Washington Post, a paper owned by Amazon CEO Jeff Bezos.