Second wild speech about Democrat is incisive (7)
I believe the answer is:
mordant
'incisive' is the definition.
(I've seen this in another clue)
'second wild speech about democrat' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'wild speech' becomes 'rant' (I've seen this in another clue).
'about' indicates putting letters inside.
'democrat' becomes 'd'.
'rant' enclosing 'd' is 'rdant'.
'mo'+'rdant'='MORDANT'
'is' is the link.
(Other definitions for mordant that I've seen before include "Corrosive" , "Biting, scathing" , "Acrimonious" , "Acerbic" , "Bitingly sarcastic" .)