Forthright Republican interrupting troublemakers at the front entrance (9)
I believe the answer is:
trenchant
'forthright' is the definition.
(I've seen this before)
'republican interrupting troublemakers at the front entrance' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'interrupting' indicates putting letters inside.
'at the front' suggests taking the first letters.
'entrance' becomes 'enchant' (to entrance is to enchant or bewitch).
The initial letter of 'troublemakers' is 't'.
't'+'enchant'='tenchant'
'r' inserted into 'tenchant' is 'TRENCHANT'.
(Other definitions for trenchant that I've seen before include "Vigorous and effective" , "Expressively incisive" , "Clear" , "Forthright, vigorous" , "Clear-cut and hard-hitting" .)