Deliberate Tory partisan (8)

I believe the answer is:

consider

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'deliberate' is the definition.
('consider' can be a synonym of 'deliberate')

'tory partisan' is the wordplay.
'tory' becomes 'con' (abbreviation for Conservative).
'partisan' becomes 'sider' (I can't justify this - if you can you should give a lot more credence to this answer).
'con'+'sider'='CONSIDER'

Can you help me to learn more?

(Other definitions for consider that I've seen before include "Deliberate" , "Reckon, deem" , "Think carefully about" , "Deem to be, regard" , "Contemplate" .)

I've seen this clue in The Telegraph.

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