Second politician, rejecting leader, left (8)
I believe the answer is:
sinister
'left' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sinister that I've seen before include "Threatening; evil-looking" , "'Ominous, baleful (8)'" , "Malign, ominous" , "Menacing" , "Resist in way that is creepy" .)