John Rood, Under Secretary of Defense for Policy at the Pentagon, is the latest senior national security official involved in the Ukraine controversy to be forced out following Trump's acquittal in the Senate impeachment trial, but sources told CNN that he broke with the administration on several issues, in addition to the handling of aid to Ukraine, leading to a loss of support from leadership.

"It is my understanding from Secretary Esper that you requested my resignation from serving as Under Secretary of Defense for Policy. Senior administration officials appointed by the President serve at the pleasure of the President, and therefore, as you have requested, I am providing my resignation effective February 28, 2020," Rood wrote in his letter to President Donald Trump, dated Wednesday.