The NRA, one of the United States' most powerful lobbying groups, headed by the actor Charlton Heston, has already agreed to scale back what was going to be a huge convention party, reducing four days of exhibitions, parties and set-piece events to just one reception, one prayer breakfast with Oliver North, the army colonel at the centre of the Iran-Contra scandal, and the meeting itself.
But Denver's liberal mayor, Wellington Webb, and his staff said this was not enough and urged citizens to call the NRA's toll-free phone number to voice their opposition to the group coming at all. "We don't want them here," said the city council president, Allegra Haynes.
One billboard advertising the NRA meeting was removed from downtown Denver, and all talk of an $18m (pounds 11m) boost to the local economy has stopped.
The NRA meeting was meant, in part, to be a celebration three new pieces of legislation in Colorado loosening restrictions on concealed weapons and making it harder for victims of shootings to sue gun manufacturers. That legislation was due to be debated on the floor of the state Capitol on Wednesday, the day after the shooting, and never even made it on to the agenda. Assemblymen simply gathered to commemorate the victims with a minute's silence and then ended the session.
Republican Doug Dean, of Colorado Springs, withdrew the two Bills he had sponsored, and Colorado's governor, Bill Owens, himself an advocate of looser gun control, said he would veto the third if it ever reached his desk.
Ever since Tuesday's shocking events, the gun lobby has been doing its utmost to behave honourably without conceding that the wide availability of firearms in affluent suburbs such as Littleton, site of Columbine High School, added to the risk of such tragedies.
The day after the shootings, Charlton Heston wrote to the 22,000 NRA members who had been expected to come to Denver, saying it was time to show "our profound sympathy and respect for the families and communities in the Denver area in their time of great loss".
He went on: "Our spirits must endure this terrible suffering together, and so must the freedoms that bring us together. We must stand in sombre but unshakable unity, even in this time of anguish."
In subsequent television interviews, however, Mr Heston sounded an altogether less conciliatory note, arguing that a teacher with a concealed weapon might have been able to curtail the violence, and expressing outrage that trench coats - the trademark clothing of the two killers and their friends - should be allowed in school on a warm spring day. "Come on. That's outrageous in a school," Mr Heston said. "I'm afraid you have to blame the parents of those two boys."
Several politicians, including Assemblyman Dean and Minnesota's flamboyant new governor, the former wrestler Jesse Ventura, shared Mr Heston's view that more weapons on campus might have helped. An armed police officer was, in fact, on campus and exchanged fire with the killers, but was powerless to overcome them.
The weapons issue is particularly divisive in Colorado because of the state's contrasting groups of liberal environmentalists and conservative, born-again Christian, hunting and shooting enthusiasts.
The battle lines manifest themselves in various ways: this is a state where no-growth ecologists are forever fighting property developers, and the liberal intellectual tradition - best represented by the prestigious University of Colorado in Boulder - clashes with fundamentalists who attend right-wing breakfast clubs and advocate home schooling for children.
Callers to right-wing Denver radio stations have argued with barely concealed rage that the school shootings have nothing to do with the guns issue and are being manipulated by the liberals for political ends.
Presenting the opposite view, three surgeons who operated on the injured made a point of saying that greater gun control would have helped to prevent the kinds of horrific wounds they had to treat. The damage done by the 9mm semi-automatic pistols used by the Columbine killers was immeasurably greater than traditional .22 calibre rifles, one said.Reuse content