Cunning leader vanishing in demo (4)

I believe the answer is:

arch

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'cunning' is the definition.
(arch can mean cunning or tricksy)

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

Can you help me to learn more?

(Other definitions for arch that I've seen before include "one under a foot?" , "Teasing; part of foot" , "Curved bony structure in the foot" , "Playfully superior" , "Embow" .)

I've seen this clue in The Telegraph, The Independent and The Sun.

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