Popular Democrat returned in strength at the end of the day (8)
I believe the answer is:
midnight
'at the end of the day' is the definition.
(I've seen this before)
'popular democrat returned in strength' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'democrat' becomes 'd'.
'returned' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'strength' becomes 'might' (might is a kind of strength).
'in'+'d'='ind'
'ind' back-to-front is 'dni'.
'dni' going inside 'might' is 'MIDNIGHT'.
(Other definitions for midnight that I've seen before include "time of transition" , "when PM finishes" , "When the day changes" , "The moment when the date changes" , "Macbeth's 'secret, black and --- hags'" .)