Today, it would be impossible to obtain a federal court order permitting a five-day protest march on a 52-mile stretch of a major U.S. highway. Under contemporary legal doctrine, the Selma protests would have ended March 8, 1965.
…Starting in the 1970s…the federal courts began rolling back this idea. A series of rulings erected what is known as the public forum doctrine, which lets a city, state or the federal government decide whether public property can be used for 1st Amendment activities. It also means that if courts do not designate a place a “traditional public forum,” government may forbid its use as a site of protest altogether.
That is from Ronald J. Krotosynszski, Jr., there is more of interest here.