Is it a crime to heckle at a campaign rally?

This question has come up with regard to recent Donald Trump-related controversies, so I thought I'd talk about it more broadly.

1. Many states outlaw "disturbing lawful assemblies," which would include campaign rallies, whether on public property or private. My own California, for instance, provides that:

Every person who, without authority of law, willfully disturbs or breaks up any assembly or meeting that is not unlawful in its character . . . is guilty of a misdemeanor.

Attempts to shut down an event, for instance by shouting down a speaker, blowing whistles so that the speaker can't be heard, rushing onto the stage and the like would thus be illegal. This is important both because the police can then arrest the disrupters, and because security guards and ordinary rally attendees could then legally use reasonable, non-deadly force to stop the disruption (more on that later).

Here's an example, from State v. Hardin (Iowa Supreme Court, 1993):

Hardin's testimony at trial revealed that he and his friends viewed the event as an opportunity to personally convey to the President [George H.W. Bush] their opposition to the government's Persian Gulf policy. Once the President began speaking, they planned to stand up and shout their concerns in turn. They then intended, in Hardin's words,

to keep chanting until we were no longer able to make our point, and I didn't know what was going to stop that. I mean, whether it was the crowd taking up a chant in response to us or kicked out or arrested. I really had no feel for what was going to happen.

At the appointed time during the President's speech, one of Hardin's friends stood up and shouted, "Bring the troops home from Saudi Arabia." Then Hardin stood and said, "Mr. President stop the build up." Another friend shouted, "No blood for oil." The trio then continued that chant. After three to five minutes, one of the event coordinators approached Hardin and asked him to sit down. Hardin said he looked at him and then "returned to what I was doing." The organizer repeated his request to no avail. The police were summoned and the three were escorted from the auditorium without further incident.

The court upheld the chanters' conviction.

2. On the other hand, it seems likely—though the case law on this is sparse—that this wouldn't apply to occasional shouts from a lone heckler, just as it wouldn't apply to expressions of approval (such as applause, shouts endorsing the speaker's message, etc.). The leading case I've seen on this is In re Kay (California Supreme Court, 1970), which held that the statute applies only when the heckler:

1. "substantially impaired the conduct of the meeting by intentionally committing acts"
2. "in violation of implicit customs or usages or of explicit rules for governance of the meeting, of which he knew, or as a reasonable man should have known,"
3. "the defendant's activity itself—and not the content of the activity's expression—substantially impairs the effective conduct of a meeting."

In re Kay concluded that, in that case, the defendants' rhythmic clapping and heckling was not punishable, when the speaker didn't ask the defendants to leave (some paragraph breaks added):

After Congressman Tunney had given a portion of his speech, a comparatively small part of the total crowd, between 25 and 250 persons, engaged in rhythmical clapping and some shouting for about five or ten minutes. This demonstration did not affect the program. Congressman Tunney, who had been using a microphone, finished his speech despite the protest, pausing to assure those protesting that they had a right to do so and to urge them to be grateful that they live in a country whose Constitution protects their right to demonstrate in that manner.

At no time did either the speaker or the police ask the protestors to be silent or to leave. Following the end of the protest and of the congressman's speech, the fireworks were shown. The police made no arrests during or immediately following the protest; the prosecution filed charges only some two weeks later….

In applying [section 403 as we have interpreted it], the nature of a meeting necessarily plays a major role. The customs and usages at political conventions may countenance prolonged, raucous, boisterous demonstrations as an accepted element of the meeting process; similar behavior would violate the customs and usages of a church service. Audience participation may be enthusiastically welcomed at a bonfire football rally or an athletic contest, but considered taboo at a solemn ceremony of a fraternal order.

Explicit rules governing the time and place of permitted nonviolent expressions may in some circumstances fix the limits of permissible conduct. Violation of such customs or rules by one who knew or as a reasonable man should have known of them would justify the application of section 403. Thus, rather than enacting monolithic standards, section 403 draws its content from the implicit customs and usages or explicit rules germane to a given meeting.

In the instant case the application of section 403 must in the first instance be examined in the light of the nature of the meeting involved here: a large, public celebration held outdoors in a public park, featuring, in the course of a political campaign, a public official as the principal speaker. Informality characterized this public rally: people could come and go as they pleased; members of the audience could move at will to other areas of the "meeting."

By custom and usage nonviolent demonstrations of political views are reasonably to be expected at such a gathering. As the evidence at trial disclosed, our history reveals that heckling and disputatious remarks at such affairs are commonplace occurrences. Indeed, the principal speaker at the rally, an elected public official, stated that the relevant custom sanctioned the demonstrative conduct of petitioners as a legitimate means of expression.

The prosecution offered no evidence that clapping, flag waving, and sloganeering are not generally accepted and permitted at a public meeting, addressed by controversial elected officials, such as the instant one. Since the nature of that meeting contemplated acceptance of the nonviolent expression of alternative viewpoints, the petitioners' protest did not impair the conduct of the meeting but instead constituted a legitimate element of it.

Moreover, the prosecution failed to show that the activities substantially impaired the conduct of the meeting. Not every violation of a general custom or of an explicit meeting rule becomes so grave as to warrant application of criminal sanctions; nor does section 403 contemplate such extensive coverage….

Whether a given instance of misconduct substantially impairs the effective conduct of a meeting depends upon the actual impact of that misconduct on the course of the meeting; the question cannot be resolved merely by asking persons present at the meeting whether they were "disturbed." In the instant case, the questioned conduct continued for only a few minutes, Congressman Tunney was able to complete his speech, and it does not appear that a large part of the audience could not hear his remarks. We conclude that the state failed to meet its burden of establishing a substantial impairment of the conduct of the meeting.

Finally, we do not believe that there was a sufficient showing that the defendants disturbed the meeting within the constitutionally permissible limits of the statutory term "disturb." Generally, if disturbances are occasioned by nonviolent exercise of free expression, section 403 will require that defendants be shown to have engaged in such conduct with knowledge, or under circumstances in which they should have known, that they were violating an applicable custom, usage, or rule of the meeting.

[Footnote, slightly moved: Meeting rules are rarely carefully spelled out or well known to the audience. In many cases these rules consist of aged and infrequently used by-laws or tacit understandings and habitual practices, or are otherwise cloaked in obscurity and uncertainty. Even if clear rules can be found, the officials of a meeting commonly suspend or simply ignore such rules to expedite the work of the meeting. Silence of meeting officials in the face of unusual or raucous activity necessarily suggests that the rules of the meeting permit the activity or that the officials do not intend to enforce prohibitory rules to the contrary….]

In instances in which the appropriate standard of conduct lies in doubt, a warning and a request that defendants curtail their conduct, either by officials or law enforcement agents, should precede arrest or citation.

See also, e.g., Dempsey v. People (Colorado Supreme Court, 2005).

3. Of course, if the event is held in a private place, and the event organizers tell the heckler to leave and the heckler doesn't leave, the heckler may be guilty of the separate crime of trespass. See, e.g., State v. Colby (Vermont Supreme Court 2009).