Downgrades protest by short trial (7)
I believe the answer is:
demotes
'downgrades' is the definition.
(I've seen this in another clue)
'protest by short trial' is the wordplay.
'protest by' becomes 'demo' (demonstration. I am not sure about the 'by' bit.).
'short' means to remove the last letter.
'trial' becomes 'test' (synonyms).
'test' with its last letter taken away is 'tes'.
'demo'+'tes'='DEMOTES'
Can you help me to learn more?
(Another definition for demotes that I've seen is " Lowers in rank".)