Before joining the Department of Defense in 2001, she had been a policy planning officer for the State Department and a Junior Fellow at the Carnegie Endowment for International Peace. A prior assignment in the DOD had been as Afghanistan Team Chief, Stability Operations Office, responsible for stability and security. In 2004 she presciently noted that to achieve these objectives, the efforts had to be enduring, with no end in sight. She identified the major needs to reach these goals: the Ministry of Defense and the Afghan National Army needed to be reformed and rebuilt to counter the resurgent Taliban and the powerful warlords; a police force was needed to combat crime; the justice system had to be assisted to ensure the rule of law; prisons had to be built. Cooper has been cognizant of women's issues. She has noted that "or much of career, it's absolutely true that been the only woman in the room quite frequently". She identifies security as a women's issue, needing their brain power to develop the best path forward. While working on Afghanistan policy, she was involved in the recruitment of the first female recruits for the National Police. Described as a "senior U.S. Department of Defense official", Cooper has been involved in multiple U.S.–Eurasian defense negotiations. She has described the Russian intervention in Ukraine as "a brazen violation of international law" after Ukrainian vessels were attacked by Russia in late November 2018. Cooper has been supportive of continued military aid to Ukraine. During a 2018 visit to Ukraine, she noted that Congress had authorized money for military aid, and she said that "one of my goals on this visit was to discuss with the Government of Ukraine what its priority needs are for security assistance." She met with Ukrainian Minister of DefenceStepan Poltorak to define measures of bilateral cooperation for defense. Cooper was the Pentagon official in charge of the aid package; she confirmed in December 2018 that the U.S. would have a comprehensive response to Russian aggression. In a video message Cooper said that Ukraine "can count on the U.S. to remain your strong partner" in strengthening its military. There is consensus that her assurances to the Ukrainians demonstrated that she expected the funds to be released in early 2019. Her testimony was sought by the Congressional committees leading the impeachment inquiry against Donald Trump in matters relating to Trump–Ukraine scandal. On October 23, 2019, in defiance to a White House letter warning her not to appear before the impeachment inquiry, Cooper testified in a closed-door deposition before congressional committees. After a five-hour delay due to a protest by Republican members of Congress, Cooper completed a 3.5 hour deposition in which she explained the process for transferring military aid to Ukraine. During a public hearing on November 20, 2019, Cooper testified to the U.S House of Representatives that Ukrainian officials knew about the hold on military aid by July 25, the day of the Trump–Zelensky call, undercutting an assertion that there could not have been a quid pro quo because Ukraine was not aware of the hold.
