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

'exercising restraint' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'republican probes top brass' is the wordplay.
I cannot really see how this works, but
'republican' could be 'r' (abbreviation) and 'r' is present in the answer.
an anagram of 'top' is 'pot' which is present in the left over letters.
an anagram of 'brass' is 'ssbra' which is within the left over letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

'about' is the link.

Can you help me to learn more?