Leaders in military uniform feel too insecure in civilian dress (5)
I believe the answer is:
mufti
'civilian dress' is the definition.
(mufti is a kind of civilian dress)
'leaders in military uniform feel too insecure' is the wordplay.
'leaders in' indicates taking the first letters.
The first letters of 'military uniform feel too insecure' is 'MUFTI'.
'in' is the link.
(Other definitions for mufti that I've seen before include "Civilian clothing; Muslim legal expert" , "Civvies; Muslim legal expert" , "Civilian gear" , "Muslim religious jurist" , "Civvy dress" .)