Isn't sure to clout conservationists (7)

I believe the answer is:

mightnt

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'isn't sure' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'clout conservationists' is the wordplay.
'clout' becomes 'might' (I've seen this before).
'conservationists' becomes 'NT' (National Trust).
'might'+'nt'='MIGHTNT'

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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