Some interesting articles on sovereign and presidential immunity

https://www.loc.gov/law/help/immunity-from-prosecution/index.php

https://digitalcommons.law.yale.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1897&context=fss_papers

http://www.tisanet.org/quarterly/3-1-13.pdf

https://scholarlycommons.law.hofstra.edu/cgi/viewcontent.cgi?article=1426&context=faculty_scholarship

https://www.justsecurity.org/wp-content/uploads/2018/05/ronaldrotunda-presidents-as-wtinesses.pdf