Support church president (6)
I believe the answer is:
pierce
'president' is the definition.
(Franklin Pierce, 14th US president)
'support church' is the wordplay.
'support' becomes 'pier' (pier is a kind of support).
'church' becomes 'CE' (abbreviation for Church of England).
'pier'+'ce'='PIERCE'
(Other definitions for pierce that I've seen before include "Not established as fact" , "Riddle" , "Make hole in for recipe" , "Skewer; run through" , "Penetrate with a sharp instrument" .)