False leaders holding power again became worse (8)
I believe the answer is:
relapsed
'again became worse' is the definition.
I can't tell whether this defines the answer.
'false leaders holding power' is the wordplay.
'false' indicates an anagram.
'holding' means one lot of letters goes inside another.
'power' becomes 'p' (symbol in physics).
'leaders' with letters rearranged gives 'relased'.
'relased' enclosing 'p' is 'RELAPSED'.
Can you help me to learn more?
(Other definitions for relapsed that I've seen before include "Failed to maintain improvement" , "having become ill again" , "Weakened" , "Regressed, got worse" , "Deteriorated in health again" .)