Republican law backed American creature (6)
I believe the answer is:
walrus
'creature' is the definition.
'republican law backed american' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'backed' is a reversal indicator.
'american' becomes 'US' (United States).
'r'+'law'='rlaw'
'rlaw' in reverse letter order is 'walr'.
'walr'+'us'='WALRUS'
(Other definitions for walrus that I've seen before include "Seal's relative" , "Carpenter's companion?" , "whiskers" , "'I am the ------', 1967 Lennon and McCartney song" , "Marine mammal with ivory tusks and a moustache" .)