[7][8][9][10][11] 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.

[14] Cooper was the Pentagon official in charge of the aid package;[15] she confirmed in December 2018 that the U.S. would have a comprehensive response to Russian aggression.

[18] Her testimony was sought by the Congressional committees leading the impeachment inquiry against Donald Trump in matters relating to the Trump–Ukraine scandal.

[19] On October 23, 2019, in defiance to a White House letter warning her not to appear before the impeachment inquiry,[20][21] 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.