Good, since cases lead to politicians finding uppermost reserve (3,3)

'cases lead to politicians finding uppermost reserve' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'good since' is the wordplay.
I cannot quite understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is located in the answer.
'since' could be 'as' (I've seen this in other clues) and 'as' is located in the answer.
The remaining letters 'cap' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?