Comment: Yes, the unbinding must take place at the State Conventions,

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In reply to comment: Rule 15 (a) (1) seems to me (see in situ)

Yes, the unbinding must take place at the State Conventions,

or whatever layer of organization placed the binding rule in effect.

If district conventions select RNC delegates directly, and the binding is from rules at that level, then that is where the unbinding needs to happen via a rule change.

If the binding is in the By-Laws for that State, or it is done via rules for the State Convention that chooses delegates, then the unbinding via a by-laws or rules change needs to happen there.

If on the other hand, the binding is by State law - forget it. That most likely can't be changed for this cycle, but it can be for the next.