Debates lacking energy in the Guardian (5)
I believe the answer is:
argus
'guardian' is the definition.
(term for a guardian, from the mythological figure)
'debates lacking energy' is the wordplay.
'debates' becomes 'argues' ('argue' can be a synonym of 'debate').
'lacking' is a deletion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'argues' with 'e' taken out is 'ARGUS'.
'in the' acts as a link.
(Other definitions for argus that I've seen before include "Type of butterfly" , "Pheasant, butterfly, a hundred-eyed monster" , "Hundred-eyed giant in mythology" , "Legendary Guardian" , "In Greek myth, a many-eyed monster slain by Hermes" .)