Worst admitting a Republican is most vacant (6)

I believe the answer is:

barest

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'most vacant' is the definition.
Both the answer and definition are superlative adjectives. Maybe there's an association between them I don't understand?

'worst admitting a republican' is the wordplay.
'worst' becomes 'best' (both can mean to beat someone).
'admitting' indicates putting letters inside.
'republican' becomes 'r' (abbreviation).
'a'+'r'='ar'
'best' going around 'ar' is 'BAREST'.

'is' acts as a link.

Can you help me to learn more?

(Another definition for barest that I've seen is " Merest".)

I've seen this clue in The Telegraph.

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