Leader in west becoming a calamity? (8)

I believe the answer is:

accident

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'calamity?' is the definition.
(calamity is a kind of accident)

I cannot understand how the rest of the clue works.

(Other definitions for accident that I've seen before include "Dance tic leading to mishap" , "Unfortunate unintentional incident" , "Eg, car crash" , "Unexpected incident" , "disaster" .)

I've seen this clue in The Sun and The Times.

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