Amassed well-informed following, competed for office (3,2)
I believe the answer is:
ran up
'amassed' is the definition.
(running up is a kind of amassing)
'well-informed following competed for office' is the wordplay.
'well informed' becomes 'up' (I've seen this in other clues).
'following' means one lot of letters go next to another.
'competed for office' becomes 'ran' (I've seen this in another clue).
'up' after 'ran' is 'RAN-UP'.
(Other definitions for ran up that I've seen before include "significant rise" , "Sewed together quickly" , "Accumulated" .)