With left coming in, can Maggie seem important? (4,5)

I believe the answer is:

loom large

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'with left coming in can maggie' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'seem important?' is the wordplay.
'seem' becomes 'loom' (looming is a kind of seeming).
'important?' becomes 'large' (similar in meaning).
'loom'+'large'='LOOM LARGE'

Can you help me to learn more?

(Another definition for loom large that I've seen is " Approach".)

I've seen this clue in The Independent.

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