First Lady Republican at all times (4)
I believe the answer is:
ever
'at all times' is the definition.
(synonyms)
'first lady republican' is the wordplay.
'first' means one lot of letters go next to another.
'lady' becomes 'eve' (woman's name).
'republican' becomes 'R' (abbreviation).
'eve'+'r' is 'EVER'.
(Other definitions for ever that I've seen before include "On any occasion" , "Always and permanent" , "Possibly" , "Always, at any time" , "At all times, always" .)