Duke, calm when upset, is not an effective type (8)

I believe the answer is:

lameduck

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'not an effective type' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'duke calm when upset' is the wordplay.
'when upset' is an anagram indicator.
'duke'+'calm'='dukecalm'
'dukecalm' anagrammed gives 'LAMEDUCK'.

'is' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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