President Trump has made wholesale changes in the Pentagon's top civilian leadership, a purge that began with the firing of Defense Secretary Mark Esper and continued Tuesday through the senior ranks.

Three top senior officials resigned on Tuesday, including the under secretaries for policy and intelligence. Esper's chief of staff also resigned. The moves sparked concern on Capitol Hill that perceived instability at the Pentagon could embolden U.S. adversaries during the presidential transition.

James Anderson, the acting under secretary for policy, the Pentagon's No. 3 spot, resigned Tuesday and was replaced by Anthony Tata, a retired Army general who once called former President Barack Obama a "terrorist leader." Tata had withdrawn his name for that Pentagon post in August before facing a contentious confirmation hearing in the Senate. He was then placed in another job that did not require a hearing.