Half-hearted regime overthrown, broken by power (5)
I believe the answer is:
tepid
'half-hearted' is the definition.
(I've seen this before)
'regime overthrown broken by power' is the wordplay.
'regime' becomes 'diet' (I've seen this before).
'overthrown' shows that the letters should be reversed in order.
'broken by' is an insertion indicator.
'power' becomes 'p'.
'diet' reversed gives 'teid'.
'teid' going around 'p' is 'TEPID'.
(Other definitions for tepid that I've seen before include "Of liquid, luke-warm" , "without enthusiasm" , "without passion" , "Half-hearted" , "Luke warm" .)