The basics of educating a trio of Republicans (5,2)

I believe the answer is:

three rs

'the basics of educating' is the definition.
(reading, writing and arithmetic)

'a trio of republicans' is the wordplay.
'a trio' becomes 'three' ('three' can be a synonym of 'trio').
'of republicans' becomes 'rs' (I can't justify this - if you can you should give a lot more credence to this answer).
'three'+'rs'='THREE RS'

I've seen this clue in The Times.

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