It's nothing for a party leader to snoop around, being silly (5)
I believe the answer is:
soppy
'being silly' is the definition.
(I've seen this before)
'it's nothing for a party leader to snoop around' is the wordplay.
'it's nothing' becomes 'O' (looks like zero - 0).
'for' says to put letters next to each other.
'a party leader' becomes 'p' (leader of the word 'party').
'to snoop' becomes 'spy' ('spy' can be a synonym of 'snoop').
'around' indicates putting letters inside.
'o'+'p'='op'
'op' inserted into 'spy' is 'SOPPY'.
(Other definitions for soppy that I've seen before include "Drenched" , "Silly" , "Over-sentimental" , "Overly sentimental" , "Mawkish" .)