The Pentagon’s top policy official, who warned against the Trump administration’s effort to block Ukraine’s military aid last year, is stepping down from his post at the end of the month, Department of Defense press secretary Alyssa Farah said in a statement. The Pentagon’s statement did not explain why John Rood, undersecretary of defense for policy, is leaving. CNN reports he was asked to resign after losing the support of national-security leaders. Farah said James Anderson, the current senior official performing the duties of the deputy undersecretary of defense for policy, will take over for Rood until President Trump has chosen a permanent successor. “I would like to thank John Rood for his service to the Department,” Secretary of Defense Mark Esper said.

Shortly after Trump’s July 25 infamous phone call with Ukrainian President Volodymyr Zelensky, Rood emailed Esper to warn that “placing a hold on security assistance at this time would jeopardize this unique window of opportunity and undermine our defense priorities with a key partner in the strategic competition with Russia.” Rood joined the Trump administration in January 2018, and was reportedly involved in certifying to Congress that Ukraine had carried out enough reforms to justify $250 million in U.S. security assistance. That certification contradicted one of the reasons put forward by some inside the Trump administration to defend blocking the delivery of aid to Ukraine.