Old measure identified by US president and English Liberal (6)

I believe the answer is:
bushel
'old measure' is the definition.
'bushel' can be an answer for 'measure' (bushel is a kind of measure). I am not certain of the 'old' bit.
'us president and english liberal' is the wordplay.
'us president' becomes 'bush' (George H W Bush or George W Bush).
'and' means one lot of letters go next to another.
'english' becomes 'E' (abbreviation).
'liberal' becomes 'l' (abbreviation).
'bush'+'e'+'l'='BUSHEL'
'identified by' acts as a link.
Can you help me to learn more?
(Other definitions for bushel that I've seen before include "Dry measure of eight gallons" , "Unit of dry or liquid measure" , "Imperial measure for grain" , "Obsolete measure (equal to 8 gallons)" , "Measure equalling eight Imperial gallons" .)