First lady, Republican to the end (4)
I believe the answer is:
ever
'to the end' is the definition.
I can't judge whether this definition defines the answer.
'first lady republican' is the wordplay.
'first' is a charade indicator (letters next to each other).
'lady' becomes 'eve' (woman's name).
'republican' becomes 'R' (abbreviation in US politics).
'eve'+'r' is 'EVER'.
Can you help me to learn more?
(Other definitions for ever that I've seen before include "Continuously" , "Perpetually" , "constantly" , "To the end of time" , "Always, at any time" .)