Is certain to ignore Republican's problem (5)
I believe the answer is:
issue
'problem' is the definition.
(I've seen this before)
'is certain to ignore republican's' is the wordplay.
'certain' becomes 'sure' (synonyms).
'to ignore' is a deletion indicator.
'republican' becomes 'R' (abbreviation).
'sure' with 'r' taken out is 'sue'.
'is'+'sue'='ISSUE'
(Other definitions for issue that I've seen before include "Topic (to be addressed)" , "Result - children" , "Bone of contention" , "Emerge" , "Contentious subject" .)