Former president wrong to be so religious (6)
I believe the answer is:
devout
'so religious' is the definition.
'devout' can be an answer for 'religious' (similar in meaning). I am unsure of the 'so' bit.
'former president wrong' is the wordplay.
'former president' becomes 'dev' (I can't explain this - if you can you should believe this answer much more).
'wrong' becomes 'out' (eg a calculation might be 'out').
'dev'+'out'='DEVOUT'
'to be' is the link.
Can you help me to learn more?
(Other definitions for devout that I've seen before include "sincere" , "Pious, earnestly religious" , "God-fearing" , "Sincerely religious" , "Pious and worshipful" .)