Limitations on this approach.
I believe that what was done here was legal, in the very narrow circumstances present.
The presidential debate was a private, restricted, invitation-only event. Invitees were vetted and searched. It was specifically not a place of public accommodation for the event.
Someone will inevitably try this same approach where the same narrow circumstances are not present. Then we'll run into an interesting legal situation. How much control does a property owner have over someone's use of the airwaves? Can an implied contract have precedence over an individual's right to use the public airwaves? Isn't there an overwhelming public policy goal to rule any such purported contract claim invalid?