Republican probes top brass about exercising restraint (6,3)

I believe the answer is:

sports bra

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'exercising restraint' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'republican probes top brass' is the wordplay.
I cannot quite understand how this works, but
'republican' could be 'r' (abbreviation in US politics) and 'r' is located in the answer.
an anagram of 'top' is 'pot' which is located in the remaining letters.
an anagram of 'brass' is 'ssbra' which is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...

'about' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

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