Old President Bush into weed? Nonsense! (7)
I believe the answer is:
hogwash
'nonsense' is the definition.
(I've seen this before)
'old president bush into weed?' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'president bush' becomes 'gw' (I can't justify this - if you can you should believe this answer much more).
'into' means one lot of letters goes inside another.
'weed?' becomes 'hash' (hash is a kind of weed).
'o'+'gw'='ogw'
'ogw' placed inside 'hash' is 'HOGWASH'.
Can you help me to learn more?
(Other definitions for hogwash that I've seen before include "Colloquial nonsense to pig cleanser" , "Baloney" , "Pigswill - nonsense!" , "Utter rubbish" , "Bunk" .)