Last politician, 51, is weak (4)
I believe the answer is:
limp
'weak' is the definition.
(I've seen this before)
'last politician 51' is the wordplay.
I cannot quite understand how this works, but
'politician' could be 'mp' (Member of Parliament) and 'mp' is present in the answer.
'51' could be 'li' (roman numeral) and 'li' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for limp that I've seen before include "obstacle to smooth progress" , "Wanting stiffness" , "Walk badly; not stiff" , "Floppy" , "Feeble" .)