Campaign events are generally not public forums, even if the candidate happens to also be an incumbent public official. For a federal official (and similar laws exist for state government), if the nexus with official government affairs required to make a public forum existed with a campaign event, that’d probably violate the Hatch Act separately from whether any violation of public forum law occurred.

Good point. If critical tweets kept him from giving his message then I expect the judge would have ruled differently.

He had not been elected yet. The moment he did, things changed.

Certainly he continues to remove hecklers from his campaign events. The distinction is a campaign event isn’t a “public forum”.