A politician's top friend creates outrage (5)
I believe the answer is:
appal
'outrage' is the definition.
(I know that outrage can be written as appal)
'a politician's top friend' is the wordplay.
'top' says to take the initial letters (in a down clue, the first letter is top).
'friend' becomes 'pal' (pal can mean a friend).
The first letter of 'politicians' is 'p'.
'a'+'p'+'pal'='APPAL'
'creates' is the link.
(Other definitions for appal that I've seen before include "Cause to be unpleasantly surprised" , "Greatly dismay" , "Dismay, horrify" , "Greatly horrify" , "Petrify" .)