Performative, is not a simple concept to explain. The adjective used mainly in linguistics and philosophy. It describes any word or statement (or action) that instantly causes the action that it describes to happen, simply by its being spoken or done.
If you say “I promise to be good.” -> the verb “promise” is performative because creates the action of “promising” -> i.e. a promise.
1976 P. Donovan Relig. Lang. vii. 80 Performative words are used, for instance, when we vote for a motion by saying ‘Aye’,..or adjourn a meeting with the words ‘The meeting is adjourned’. [Ed. the whole sentence "The meeting is adjourned" is performative.]
There is an aphorism: “The word is the deed” -> (Current Modern English) The word is the action or thing -> "The word is performative." This is the basic meaning of performative.
This performative aspect in A and B does not occur in “I can see the dog,” which is a statement of the experience that you had a moment before you said the sentence. The dog was not created by your words, it was always there.
Trump's power is based on performative cruelty. -> Trump's power is based the exercise of that power that automatically causes cruelty to be done/an instance of cruelty to arise.
That would mean that the word "performative" were superfluous in all its uses - the answer must be "No, it is not superfluous."
It does not at all mean "Trump's power is based on cruelty".
Trump's power is based on performative cruelty. -> Trump's power is based on power that automatically causes cruelty and/or cruelty to arise.
I would read "performative" — using the "popular" meaning of the word — as meaning that it is done "for show": Policies and actions are visibly cruel because his base approves of such overtly callous and punitive approach.
Trump politically benefits not necessarily from cruel policies but from policies that are seen to be cruel, harsh, or overtly heavy-handed.