Republican Party upset with overseas parasite toy (4,5)

I believe the answer is:

pogo stick

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'toy' is the definition.
(I know that pogo stick is a type of toy)

'republican party upset with overseas parasite' is the wordplay.
'republican party' becomes 'GOP' (Grand Old Party, nickname for the Republican Party).
'upset' is a reversal indicator.
'with overseas' becomes 'os' (I can't explain this - if you can you should give a lot more credence to this answer).
'parasite' becomes 'tick' (type of parasite).
'gop' written backwards gives 'pog'.
'pog'+'os'+'tick'='POGO STICK'

Can you help me to learn more?

(Other definitions for pogo stick that I've seen before include "Jumping toy" , "On which kids bounce along" , "Jumping rod with a spring" .)

I've seen this clue in the Sydney Morning Herald.

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