Unsophisticated Republican (American model) in charge (6)
I believe the answer is:
rustic
'unsophisticated' is the definition.
(I know that unsophisticated can be written as rustic)
'republican american model in charge' is the wordplay.
'republican' becomes 'R' (abbreviation).
'american' becomes 'US' (United States).
'model' becomes 'T' (Ford Model T car).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'r'+'us'+'t'+'ic'='RUSTIC'
(Other definitions for rustic that I've seen before include "someone to represent the country?" , "Of the country, bucolic" , "Country bumpkin" , "Rural, country" , "Peasant; roughly made" .)