Projectile shot over president's party (7)
I believe the answer is:
torpedo
'projectile' is the definition.
(I have seen 'Underwater projectile' mean 'torpedo' so perhaps 'projectile' could also mean 'torpedo')
'shot over president's party' is the wordplay.
'shot' becomes 'tore' ('tear' can be a synonym of 'shoot'**).
'over' indicates putting letters inside.
'president' becomes 'p' (common abbreviation eg in VP).
'party' becomes 'do' (do is a kind of party).
'tore' enclosing 'p' is 'torpe'.
'torpe'+'do'='TORPEDO'
(Other definitions for torpedo that I've seen before include "Trooped off with underwater missile" , "electric ray" , "Sea-borne missile" , "attack" , "Weapon travelling under water" .)