Ascent is difficult for the poor (4-2)

I believe the answer is:

hard-up

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

'poor' is the definition.
(similar in meaning)

'ascent is difficult' is the wordplay.
I cannot really understand how this works, but
'difficult' could be 'hard' (synonyms) and 'hard' is present in the answer.
The remaining letters 'up' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'for the' is the link.

Can you help me to learn more?

(Another definition for hard-up that I've seen is " Impoverished".)

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

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