The Guardian’s Julian Borger has background on Marie Yovanovitch:
Since leaving Kyiv, Yovanovitch has been on sabbatical at the Institute for the Study of Diplomacy at Georgetown University, but is still a serving foreign service officer.
Her reported decision to appear seems to be in defiance of a block imposed by the secretary of state, Mike Pompeo, ordering state department officials not to give depositions to the congressional impeachment hearings. It is unclear whether the Trump administration will take further measures to try to stop her, in which case the Democrats running the House committees leading the impeachment investigation have signaled they are ready to issue friendly subpoenas.
First Pompeo yanks her out of Ukraine at Trump’s behest, … Read the rest