Crossword Genius

One politician in difficult issue (3)

Ross

I believe the answer is:

imp

I'm a little stuck... Click here to teach me more about this clue!

'difficult issue' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'one politician' is the wordplay.
'one' becomes 'i' (Roman numeral).
'politician' becomes 'MP' (Member of Parliament).
'i'+'mp'='IMP'

'in' is the link.

Can you help me to learn more?

(Other definitions for imp that I've seen before include "Scallywag" , "Mischievous fairy No.1" , "Scamp" , "one likely to cause trouble" , "Mischievous monkey" .)

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