The First Amendment protects a campaign’s ability to control its political message. That’s why political candidates generally have the right to kick protesters out of campaign rallies. But when it happens, the decision may reveal as much about the candidate’s values as anything he or she says explicitly.

Rallies are political theater, and a campaign that has rented space for a rally can declare someone to be a trespasser in that space, and have him or her ejected, if that person’s presence interferes with the campaign’s chosen message.

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This has happened several times during this election season — and not just at the rallies of Donald Trump. (Though it is, to be sure, a repeat occurrence at Trump rallies). Bernie Sanders’ staff ejected a man wearing a Donald Trump shirt from a rally in Massachusetts in January, for example, and Black Lives Matter activists were kicked out of a Hillary Clinton rally in Georgia in February. As long as the exclusion is not based on a characteristic protected by nondiscrimination laws — such as race, gender, or religion — a campaign can use the trespass laws to control its message, whatever that message may be.

For precisely this reason, a candidate’s choice to eject protesters from a political rally can tell us quite a bit about that candidate’s values — sometimes, even more than the candidate may openly admit. Take, as a particularly enlightening example, the Trump campaign’s ejection of protesters from his Portland, Maine rally last Thursday. These protesters stood silently and held up pocket Constitutions while Trump spoke, and were promptly escorted out of the rally by campaign staff.

It was the Trump campaign’s right to decide that the message these Constitution bearers intended to convey — the importance of Constitutional rights, say, or solidarity with the families of fallen soldiers — was incompatible with its political theater. And the campaign had the right to protect its own brand by ejecting them, pocket Constitutions and all, from the rally.

Trump has made no secret of his hostility towards certain Constitutional rights, as the ACLU explained in its legal analysis, Donald Trump: A One-Man Constitutional Crisis. This hostility even extends to the right of free expression — which is precisely what guarantees him the ability to exclude protesters from his rallies.

But make no mistake about it: The exclusion of protesters is itself an expressive act, and in an age of rampant obfuscation by political candidates, it can supply much needed evidence of a candidate’s actual views.