Conservative Republican is double trouble (6)
I believe the answer is:
crisis
'trouble' is the definition.
'conservative republican is double' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'republican' becomes 'r' (abbreviation).
'double' shows that letters should be duplicated.
'is' doubled is 'isis'.
'c'+'r'+'isis'='CRISIS'
(Other definitions for crisis that I've seen before include "time of distress" , "Climacteric" , "Dilemma" , "Critical point" , "Crucial point - decision time" .)