Broadcast by single politician causes damage (6)
I believe the answer is:
impair
'damage' is the definition.
(I know that impair is a more specific form of damage)
'broadcast by single politician' is the wordplay.
'broadcast' becomes 'air' (to air on TV).
'by' is a charade indicator (letters next to each other).
'single' becomes 'I' (one).
'politician' becomes 'MP' (Member of Parliament).
'i'+'mp'='imp'
'air' put after 'imp' is 'IMPAIR'.
'causes' acts as a link.
(Other definitions for impair that I've seen before include "Courteous man (colloq.)" , "Harm" , "'Mar, spoil (6)'" , "Hurt or handicap" , "blunt" .)