President Calvin ____ (8)
I believe the answer is:
coolidge
'president calvin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for coolidge that I've seen before include "Calvin --, US president" , "follower of Calvin" , "US president of the 1920s" , "Head of state" , "Calvin . . . . . . . ., 30th president of the USA" .)