Lecture 50% of voters (5)
I believe the answer is:
orate
'lecture' is the definition.
(I've seen this before)
'50% of voters' is the wordplay.
'50% of' suggests halving the letters.
'voters' becomes 'electorate' (I've seen this in another clue).
'electorate' halved is 'ORATE'.
(Other definitions for orate that I've seen before include "Pontificate" , "Speak in florid style" , "Speak publicly" , "Speak in public" , "Speechify" .)