Does the right of the people peaceably to assemble apply to peaceful members of a group that partially becomes violent?

Question

If John, Alice, and a bunch of other people are peacefully protesting, and then John and some others start acting violently, does the First Amendment give Alice and the others the right to continue protesting peacefully, or can the police make all of the protesters stop?

Answer 1

It depends on the circumstances. The police cannot order people to stop protesting, but they can order people to stop rioting.

One extreme, which the courts have never imposed on law enforcement, would be that you can only order a person to cease / disperse if the officer observes them committing a crime. Another extreme, which the courts have never sanctioned, is that if a single individual commits a crime, all individuals in that group can be ordered to stop protesting. The line between these two extremes is drawn at higher levels (the mayor and/or chief of police), with an eye towards strict-scrutiny considerations plus political blow-back (which we will ignore here). The default legal assumption is that the protest action is legal, therefore it must be allowed to continue.

An official dispersal order might be given, in accordance with the operating procedures of the law enforcement unit involved, e.g. 2 years ago in Portland. Here is a draft of Directive 0635.10 (the underlying Portland policy), currently under review.

The guidelines on ordering the cessation of a demonstration are driven by strict-scrutiny considerations. You have a First Amendment right to protest. The government has a compelling interest in protecting people and property. Infringement of that First Amendment right must be narrowly tailored to achieving that goal and must be the least restrictive. A highly-restrictive policy of only arresting people in the act can, in some circumstances (Portland, Seattle etc), be ineffective for achieving that compelling state interest, though there remains (some, minor) political debate over whether police should have issued dispersal orders earlier and more often.