Explicit sex possibly involves president (7)
I believe the answer is:
express
'explicit' is the definition.
(similar in meaning)
'sex possibly involves president' is the wordplay.
'possibly' indicates an anagram.
'involves' is an insertion indicator.
'president' becomes 'pres' (I can't explain this - if you can you should give a lot more credence to this answer).
'sex' is an anagram of 'exs'.
'exs' enclosing 'pres' is 'EXPRESS'.
Can you help me to learn more?
(Other definitions for express that I've seen before include "Put into words - high speed" , "Squeeze out - speak" , "Utter - non-stop" , "Utter - direct" , "for a specific purpose?" .)