The top Russia official on President Trump’s National Security Council is planning to step down from his post, NPR reports. Tim Morrison is scheduled to testify on Thursday in the impeachment inquiry, but has not been subpoenaed to testify. It is not clear whether Morrison was asked to step down, or departed of his own accord. Morrison is a protege of former White House National Security Adviser John Bolton, who has also been asked to testify by House Democrats. Morrison departed his longtime position as policy director for the Republican staff on the House defense panel in July to work for Bolton on the NSC.

The NSC is the White House body at the helm of contact with Russia. As the senior director responsible for that region, Morrison’s testimony could be critical to House Democrats’ efforts to understand President Trump’s alleged pressure on Ukrainian president Volodymyr Zelensky to pursue an investigation into Joe Biden and his son while nearly $400 million in military aid was withheld. “If there was a quid pro quo, (Morrison) would know,” one former NSC official in the Trump administration told NPR. “He would know if there is a hold on military assistance.”