Partisan loyalty on organised trip so typical (5,8)
I believe the answer is:
party politics
'partisan loyalty' is the definition.
(loyalty to a political party)
'organised trip so typical' is the wordplay.
'organised' indicates an anagram.
'trip'+'so'+'typical'='tripsotypical'
'tripsotypical' with letters rearranged gives 'PARTY POLITICS'.
'on' acts as a link.
(Other definitions for party politics that I've seen before include "Something MPs adhere to" , "Typical tripos (anag)" , "Squabbling in evidence at 21's 19 20" , "Parliamentary activity not marked by strong principles?" .)