Wealthiest Republican and I got treasure box (7)
I believe the answer is:
richest
'wealthiest' is the definition.
('rich' can be similar in meaning to 'wealthy')
'republican and i got treasure box' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'and' means one lot of letters go next to another.
'got' is a charade indicator (letters next to each other).
'treasure box' becomes 'chest' (I've seen this in another clue).
'r'+'i'+'chest'='RICHEST'
(Other definitions for richest that I've seen before include "Having the most, money say" , "Least likely to be a beggar" , "most valuable" , "Most wealthy" , "Wealthiest" .)