Jokes about youth, Republican, in best clothes (4,4)
I believe the answer is:
glad rags
'best clothes' is the definition.
(I've seen this before)
'jokes about youth republican' is the wordplay.
'jokes' becomes 'gags' (gagging is a kind of joking).
'about' means one lot of letters goes inside another.
'youth' becomes 'lad' (I've seen this before).
'republican' becomes 'r' (abbreviation).
'lad'+'r'='ladr'
'gags' going around 'ladr' is 'GLAD RAGS'.
'in' is the link.
(Other definitions for glad rags that I've seen before include "Best bib and tucker" , "Fancy clothes for laggards" , "best suit" , "What partygoers showed up in" , "Smart clothes (for a special occasion)" .)