Potential danger by the barrelful (6,3)

I believe the answer is:

powder keg

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'potential danger' is the definition.
'powder keg' can be an answer for 'danger' (powder keg is a kind of danger). I am unsure of the 'potential' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for powder keg that I've seen before include "Potential source of explosive violence?" , "Potentially explosive situation?" , "potential disaster" , "Volatile situation" , "Barrel for holding explosive" .)

I've seen this clue in The Globe and Mail.

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