Native American's adopting Democrat moral codes (6)
I believe the answer is:
creeds
'moral codes' is the definition.
'native american's adopting democrat' is the wordplay.
'native american's' becomes 'cree's' (an indigenous people of North America).
'adopting' means one lot of letters goes inside another (inserted letters are taken on or adopted).
'democrat' becomes 'd'.
'crees' placed around 'd' is 'CREEDS'.
(Other definitions for creeds that I've seen before include "Church writings" , "Statements of belief" , "Beliefs and religions" , "Systems of beliefs" .)