Worry about party showing quality of character (7)
I believe the answer is:
calibre
'quality of character' is the definition.
(I've seen this before)
'worry about party' is the wordplay.
'worry' becomes 'care' (eg without a care means without a worry).
'about' means one lot of letters goes inside another.
'party' becomes 'lib' (abbreviation for Liberal, uk political party).
'care' enclosing 'lib' is 'CALIBRE'.
'showing' acts as a link.
(Other definitions for calibre that I've seen before include "Diameter of bore of firearm" , "gifts" , "Quality of character" , "Ability; barrel diameter" , "Quality - gun barrel bore" .)