Presumptuous president once torn apart by conflict (7)
I believe the answer is:
forward
'presumptuous' is the definition.
(similar in meaning)
'president once torn apart by conflict' is the wordplay.
'president once' becomes 'ford' (Gerald Ford).
'torn apart by' indicates putting letters inside (some letters tear an opening in others).
'conflict' becomes 'war' (war is a kind of conflict).
'ford' enclosing 'war' is 'FORWARD'.
(Other definitions for forward that I've seen before include "Promote" , "To the front" , "Attacking player" , "Dispatch" , "Pushy - send (on)" .)