About Sunak's lacking height: it's a major problem (6)

I believe the answer is:

crisis

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'major problem' is the definition.
(I've seen this in another clue)

I don't understand the remainder of the clue.

(Other definitions for crisis that I've seen before include "Emergency or turning point" , "Climax, breaking point" , "Emergency (in midlife?)" , "Turning point or crux" , "A decisive or dangerous time" .)

I've seen this clue in The Independent.

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