One’s associated with a former politician’s excuses (6)
I believe the answer is:
alibis
'excuses' is the definition.
(alibiing is a kind of excusing)
'one's associated with a former politician's' is the wordplay.
'one's' becomes 'is' (Roman numeral).
'associated with' says to put letters next to each other.
'former politician' becomes 'lib' (member of the Liberal Party).
'a'+'lib'='alib'
'is' put after 'alib' is 'ALIBIS'.
(Other definitions for alibis that I've seen before include "Proofs of absence from the scene of the crime" , "Defences of being elsewhere at times of crimes" , "Defences in court" , "Defences of being elsewhere at the time of a crime" , "Pleas of being elsewhere at the time of a crime" .)