The 20-year-old gunman who opened fire in a Connecticut elementary school Friday morning carried the kind of semiautomatic weapons that have become the bloody hallmark of the American gun massacre — and perpetual exhibits in the cyclical and never resolved debate about gun control that follows every similar killing spree.

The killing of 20 children in their school prompted fresh and sometimes anguished calls to toughen the country’s gun laws. But the history of previous shootings suggests that the hard politics of the issue always trump the grief of the moment.

“As we mourn, we must sound a call for our leaders to stand up and do what is right,” said Capt. Mark Kelly, the husband of former congresswoman Gabby Giffords (D-Ariz.), who was seriously wounded in a mass shooting in Tucson in 2011 that killed six and wounded 13. “This time, our response must consist of more than regret, sorrow and condolence. The children of Sandy Hook Elementary School and all victims of gun violence deserve leaders who have the courage to participate in a meaningful discussion about our gun laws — and how they can be reformed and better enforced to prevent gun violence and death in America. This can no longer wait.”

But others immediately cautioned against a hasty legislative response. “I think we have to be careful about new, suggesting new gun laws,” Rep. Cathy McMorris Rodgers (R-Wash.), the incoming chairman of the House Republican Conference. “We need to look at what drives a crazy person to do these kind of actions and make sure that we’re enforcing the laws that are currently on the books. And yes, definitely, we need to do everything possible to make sure that something like this never happens again.”

A spokesman for the National Rifle Association said that “until the facts are thoroughly known, NRA will not have any comment.”

The National Shooting Sports Foundation, the gun manufacturers’ trade group, which is headquartered in Newtown, the town where the killings occurred, said in a statement: “Our hearts go out to the families of the victims of this horrible tragedy in our community.”

The foundation, which runs the country’s largest trade gun show in Las Vegas each year, said it would have no further comment “out of respect for the families, the community and the ongoing police investigation.”

Adam Lanza walked into the school where his mother taught with two handguns, a Glock and a Sig Sauer, according to law enforcement officials. Lanza also possessed a .223 Bushmaster rifle, a semiautomatic assault weapon, but it still is unclear whether he brought it into the school.

Six adults were shot dead at the school. Another body, believed to be Lanza’s mother, was found at a house in Newtown.

A law enforcement source said Lanza possibly obtained the weapons from a family member. He fired “dozens and dozens of shots,” said another law enforcement source.

The Glock is serially employed in mass shootings: It was used in the Tucson shooting, at the 2007 Virginia Tech shooting that killed 32 people and wounded 27 others, and at the movie theater shooting in Aurora, Co., in July that left 12 people dead and 58 wounded at the midnight show.

The Sig Sauer was used in a 1989 shooting in Louisville that left eight people dead and 12 wounded. And the Bushmaster was the weapon used by the Washington snipers John Allen Muhammad and Lee Boyd Malvo, who terrorized the metropolitan area in 2002, killing 10 people and critically wounding three.

President Obama said Friday that “we’re going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics.”

New York Mayor Michael Bloomberg, a longtime advocate of gun control, responded that “President Obama rightly sent his heartfelt condolences to the families in Newtown. But the country needs him to send a bill to Congress to fix this problem. Calling for ‘meaningful action’ is not enough. We need immediate action. We have heard all the rhetoric before. What we have not seen is leadership — not from the White House and not from Congress. That must end today.”

Recent mass shootings have not spurred support for stricter gun laws. An August Washington Post-Kaiser Family Foundation poll shortly after the mass shooting in Aurora found 51 percent supporting stricter gun laws, almost unchanged from 52 percent in January 2011. That Washington Post-ABC News poll found that a 57 percent majority supported banning high-capacity ammunition clips with more than 10 bullets, but two-thirds opposed an across-the-board ban on handgun sales.

Some polling suggests that Americans view high-profile shootings as isolated events, not evidence of a broader problem in American society.

Some activists said the sight of dead children could change public opinion and the political atmosphere.

“It could spur an effort” to pass gun control legislation, said Kristen Rand, the legislative director of Violence Policy Center. “It may be harder for the NRA to say no. And for the [National Shooting Sports Foundation], which has been at the forefront of efforts to rebrand assault rifles as modern sporting rifles.”

Polling analyst Scott Clement contributed to this report.