Broadcast by single politician causing damage (6)
I believe the answer is:
impair
'damage' is the definition.
(impairing is a kind of damaging)
'broadcast by single politician' is the wordplay.
'broadcast' becomes 'air' ('air' can be a synonym of 'broadcast').
'by' is a charade indicator (letters next to each other).
'single' becomes 'i' (one).
'politician' becomes 'mp'.
'i'+'mp'='imp'
'air' put after 'imp' is 'IMPAIR'.
'causing' acts as a link.
(Other definitions for impair that I've seen before include "Spoil strength, quality of" , "Reduce" , "Spoil, degrade" , "Courteous man (colloq.)" , "'Mar, damage (6)'" .)