Obama ordered drone strikes that intentionally killed at least two Americans. One he copped to, one he denied was intentional.
https://en.wikipedia.org/wiki/Anwar_al-Awlaki
https://en.wikipedia.org/wiki/Killing_of_Abdulrahman_al-Awla...
To my mind, that is exactly the sort of thing I'd like to be hamstrung by a fear of prosecution.
(Trump ordered drone a drone strike that also killed Abdulrahman's eight-year-old American sister.)