Proof includes camera rolls featuring a politician’s plan to discredit (5,8)
I believe the answer is:
smear campaign
'plan to discredit' is the definition.
(campaign designed to discredit someone)
'proof includes camera rolls featuring a politician's' is the wordplay.
'proof' becomes 'sign' ().
'includes' is an insertion indicator.
'rolls' is an anagram indicator (letters move or roll into new positions).
'featuring' is an insertion indicator.
'politician' becomes 'mp' (Member of Parliament).
'camera' anagrammed gives '[camera]'.
'sign' going around '[camera]' is 's[camera]ign'.
'a'+'mp'='amp'
'smearcaign' placed around 'amp' is 'SMEAR CAMPAIGN'.
(Other definitions for smear campaign that I've seen before include "Concerted operation to sully someone's name" , "Manager is camp (anag)" , "Organised attempt at defamation" , "Course of action to discredit someone" , "Negative propaganda aimed at damaging a person's reputation" .)