In short order, the race was infused with fresh calls to ban bump stocks, outlaw military-style weapons like the AR-15 and eliminate loopholes for sales at gun shows.
Mr. Heenan, one of the candidates in the race, soon released an essay apologizing for not giving “a more straightforward answer” to a grandmother who had asked him how he would help prevent gun violence.
Another candidate, Kathleen Williams, made prevention of gun massacres central to her platform, and later said, “If the N.R.A. wants to give me an F for that, then I will proudly stand with all of you and say that F means ‘fearless.’ ”
Lynda Moss, who is also running for the seat, spoke this week about a column she wrote years ago, when she described “how Montana’s gun policies became a facade of the N.R.A. — a false front used to broadcast fear and misinformation perpetuating the myth of the Wild West.”
Some supporters of gun rights said they were skeptical that attacking the N.R.A. would do any of the candidates much good in a state like Montana, where gun ownership is deeply entwined with the state’s history and culture.
“In Montana, every candidate is going to say, ‘I’m going to support the Second Amendment’ — and then some will add, ‘but,’ ” said Gary Marbut, the president of the Montana Shooting Sports Association, who has helped push nearly 70 gun rights bills into state law since the 1980s. The suddenly vocal critics of the N.R.A., he said, were “clearly political opportunists.”
The group backed the Republican incumbent in the House race, Greg Gianforte, in a special election in 2017 and is expected to do so again this year, when he is favored to win re-election. Neither the N.R.A. nor Mr. Gianforte’s campaign responded to requests for comment for this article.