Introduce President's first fantastic decree (7)
I believe the answer is:
precede
'introduce' is the definition.
(I know that introduce can be written as precede)
'president's first fantastic decree' is the wordplay.
'president's first' becomes 'p' (1st letter of 'president').
'fantastic' indicates anagramming the letters (a fantastic or improbable ordering of the letters).
'decree' anagrammed gives 'recede'.
'p'+'recede'='PRECEDE'
(Other definitions for precede that I've seen before include "go before the others" , "Take the lead" , "Having to come in front" , "Forerun" , "Come before (something)" .)