Old belligerent Republican: last of the Washington crop (7)
I believe the answer is:
redcoat
'old belligerent' is the definition.
(historical term for a British soldier)
'republican last of the washington crop' is the wordplay.
'republican' becomes 'r' (abbreviation).
'last of' says to take the final letters.
'washington' becomes 'dc' (Washington DC).
'crop' becomes 'oat' (type of plant).
The final letter of 'the' is 'e'.
'r'+'e'+'dc'+'oat'='REDCOAT'
(Other definitions for redcoat that I've seen before include "British soldier or Butlin's worker" , "Old British soldier - Butlin's entertainment organiser" , "Do react (anag) - old soldier" , "camp entertainer" , "British soldier in the American War of Independence" .)