Charge one politician with a piece of treachery (7)
I believe the answer is:
impeach
'charge' is the definition.
(I know this)
'one politician with a piece of treachery' is the wordplay.
'one' becomes 'I' (Roman numeral).
'politician' becomes 'MP' (Member of Parliament).
'with' is a charade indicator (letters next to each other).
'a piece of treachery' becomes 'each' (I can't justify this - if you can you should give a lot more credence to this answer).
'i'+'mp'+'each'='IMPEACH'
Can you help me to learn more?
(Other definitions for impeach that I've seen before include "Charge with major crime" , "Arraign, charge" , "Arraign - revile" , "Charge public official with misconduct - Clinton?" , "Charge with treason, etc" .)