Perplex and briefly astound politician (5)
I believe the answer is:
stump
'perplex' is the definition.
(I know that stump is a kind of perplex)
'briefly astound politician' is the wordplay.
'briefly' means to remove the last letter.
'astound' becomes 'stun' (I've seen this in another clue).
'politician' becomes 'MP' (Member of Parliament).
'stun' with its last letter taken away is 'stu'.
'stu'+'mp'='STUMP'
'and' acts as a link.
(Other definitions for stump that I've seen before include "Truncated trunk" , "Confound" , "Remains of tree - puzzle" , "Nonplus" , "Fox" .)