“I obviously don't dispute that the president has the right to withdraw an ambassador at any time, for any reason,” Ms. Yovanovitch said under questioning by Ohio Republican Brad Wenstrup. “But what I do wonder is why it was necessary to smear my reputation, falsely?”

The President's Twitter outburst Friday creates a dangerous situation for current foreign-service staff abroad, said Brett Bruen, a former diplomat who served as director of engagement in the Obama White House. It gives foreign leaders “carte blanche to go after ... our most senior diplomats overseas, because the President did it.”​