Bush and Biden primarily talk rubbish (7)
I believe the answer is:
bramble
'bush' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bramble that I've seen before include "Blackberry shrub" , "Wild thorny shrub" , "Thorny bush" , "Blackberry plant" , "berries" .)