Republican in disreputable club shows ambition (5)
I believe the answer is:
drive
'ambition' is the definition.
(thesaurus)
'republican in disreputable club' is the wordplay.
'republican' becomes 'r' (abbreviation).
'in' means one lot of letters goes inside another.
'disreputable club' becomes 'dive'.
'r' put within 'dive' is 'DRIVE'.
'shows' is the link.
(Other definitions for drive that I've seen before include "Avenue" , "Propel; outing" , "Ambition - steer" , "spin" , "Control and steer vehicle" .)