President stuck in part of trousers: ride to the rescue! (4,2,6)
I believe the answer is:
turn up trumps
'ride to the rescue' is the definition.
(both can mean to perform well when needed)
'president stuck in part of trousers' is the wordplay.
'president' becomes 'trump' (Donald Trump).
'stuck in' indicates putting letters inside.
'part of trousers' becomes 'turn-ups' (turned up ends of trousers).
'trump' inserted inside 'turnups' is 'TURN UP TRUMPS'.
(Other definitions for turn up trumps that I've seen before include "In bezique, one must" , "be especially helpful" , "In whist, you will have to" , "behave unexpectedly generously" .)