In one term all leaders make a little bit (4)
I believe the answer is:
iota
'a little bit' is the definition.
(I've seen this before)
'in one term all leaders' is the wordplay.
'leaders' indicates taking the first letters.
The first letters of 'in one term all' is 'IOTA'.
'make' is the link.
(Other definitions for iota that I've seen before include "Tiny piece" , "Just a jot, like Greek letter" , "Ninth letter of Greek alphabet, small amount" , "Old letter" , "Smidgeon" .)