Unhinged senatorial explanations (10)

I believe the answer is:

rationales

I'm a little stuck... Click here to teach me more about this clue!

'explanations' is the definition.
(rationale is a kind of explanation)

'unhinged senatorial' is the wordplay.
'senatorial' can be anagrammed to 'RATIONALES'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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