Candidates initially stay calm about disaster (9)
I believe the answer is:
cataclysm
'disaster' is the definition.
(I know that disaster can be written as cataclysm)
'candidates initially stay calm about' is the wordplay.
'initially' says to take the initial letters.
'about' is an anagram indicator.
The initial letter of 'candidates' is 'c'.
'stay'+'calm'='staycalm'
'staycalm' with letters rearranged gives 'ataclysm'.
'c'+'ataclysm'='CATACLYSM'
(Other definitions for cataclysm that I've seen before include "Event resulting in great loss and misfortune" , "Disastrous upheaval or flood" , "A clam cyst could be a disaster" , "Calamity" , "A violent upheaval or disaster" .)