A little drink is wrong for a political leader (3)
I believe the answer is:
sip
'a little drink' is the definition.
(I've seen this in another clue)
'is wrong for a political leader' is the wordplay.
'wrong' indicates an anagram.
'for' means one lot of letters go next to another.
'leader' indicates taking the first letters.
The first letter of 'political' is 'p'.
'is' is an anagram of 'si'.
'si'+'p'='SIP'
(Other definitions for sip that I've seen before include "Smallest drink" , "Take in slowly" , "Small mouthful of fluid" , "Drink, small mouthful" , "Drink slowly" .)