The Peoples Republic of Boulder has an anti-gun measure before the city council right now that so far has garnered opposition in the council meeting, and a protest out on the street. The outdoor protest happened in spite of inclement weather and at least some aspects of it such as open carry of firearms were already banned in Boulder. The police took a neutral view of this and limited actions to informing people of the relevant Boulder ordinances.
The city council has been sufficiently alarmed by public opposition to their proposed "assault weapon" ban that one of the bills supporters is now opposing a suggestion to put the measure on the ballot this November to let the public decide. Seems he doesn't think the public can be trusted to limit their civil rights in a politically correct manner and is asking that the measure be passed by the council without any further input from the peasants as quickly as possible.
Bloombergs sock puppet groups are also worried that if the measure is not rammed through quickly, there will be more demonstrations and public sentiment will be swayed to support the second amendment.
Restraint shown by the police in the face of a peaceful gathering is certainly laudable with no word as yet as to whose idea that was. I suspect that had the demonstration been one by say Antifa that involved rock throwing, assaults, and the burning of a building, that the Mayor would have told the police and fire departments to stand down rather than risk infringing anyones civil rights to free speech.