Barred door at front opening on behalf of US President (9)
I believe the answer is:
forbidden
'barred' is the definition.
(thesaurus)
'door at front opening on behalf of us president' is the wordplay.
'at front' says to take the initial letters.
'opening' means one lot of letters goes inside another (some letters open a gap in others).
'on behalf of' becomes 'for' (I've seen this before).
'us president' becomes 'Biden' (Joe Biden).
The initial letter of 'door' is 'd'.
'for'+'biden'='forbiden'
'd' going into 'forbiden' is 'FORBIDDEN'.
(Other definitions for forbidden that I've seen before include "Proscribed" , "This fruit is always more enticing" , "not 35 [PERMISSIBLE]" , "Not allowed, banned" , "Disallowed, banned" .)