Former Rep. Gabrielle Giffords, who was shot in the head during a mass shooting in Tucson, Ariz., exactly two years ago, has stepped into the national spotlight to offer a one-word opinion about US gun violence: "Enough."

The comment is part of an interview with ABC set to be aired Tuesday night, and it comes as Ms. Giffords and her astronaut husband, Mark Kelly, announced the formation of a new group aimed at influencing the national debate on gun violence and countering the political and financial influence of the National Rifle Association (NRA). The goal, the couple wrote in USA Today Tuesday, is to ensure that "legislators will no longer have reason to fear the gun lobby."

The national tragedy that played out at Sandy Hook Elementary School in Newtown, Conn., on Dec. 14, has shifted the tenor and substance of the debate over the Second Amendment, which guarantees the rights of Americans to own and carry firearms, for the first time in decades. And Giffords, with her own heroic story of recovery, could be uniquely placed to help marshal gun-control forces moving forward.

The decision by Giffords, herself a gun owner and a supporter of the Second Amendment, shows a sense of urgency in capitalizing on post-Newtown emotions. The Obama administration, too, is trying to move quickly – this week initiating conversations with gunmakers, Hollywood producers, gun-crime victims, and gun rights groups about how to proceed. But the efforts risk exposing cracks in a notably fractious gun-control movement.

[Editor's note: The original version of this story misstated Ms. Gifford’s position on the Second Amendment.]

"One of the things that the gun-control movement has always faced is an abundance of underfunded groups that don't work together well," says Duke University gun-policy expert Kristin Goss, author of "Disarmed: The Missing Movement for Gun Control in America." "But that's gotten better in recent years. These groups are now working together more sympathetically, and the arrival of [New York Mayor] Michael Bloomberg on the scene can't be underestimated, where he's got a national platform, deep pockets, and is completely unafraid of the NRA."

In evidence of this improving coordination, Giffords and Mr. Kelly traveled both to Newtown to meet with parents and to New York to discuss their plans with Mayor Bloomberg before deciding to launch their group, which will be called Americans for Responsible Solutions.

In the ABC News interview, Kelly says he almost "lost it" when a Newtown parent showed him a picture of a slain Sandy Hook student.

"In response to a horrific series of shootings that has sown terror in our communities, victimized tens of thousands of Americans, and left one of its own bleeding and near death in a Tucson parking lot, Congress has done something quite extraordinary – nothing at all," Giffords and Kelly wrote in USA Today.

"This country is known for using its determination and ingenuity to solve problems, big and small. Wise policy has conquered disease, protected us from dangerous products and substances, and made transportation safer. But when it comes to protecting our communities from gun violence, we're not even trying – and for the worst of reasons," they added.

After failing for decades to budge Americans' general support for gun rights, gun-control advocates now see a major opening after Newtown, where 20 schoolchildren and six staffers were killed in a blizzard of high-powered rifle fire before the gunman, 20-year-old Adam Lanza, took his own life.

Unlike other mass shootings, including the Tucson incident in which Giffords was injured and six others died, the Newtown massacre appeared to have actually changed American opinions on gun rights and gun control. On Dec. 20, a CBS News poll found an 18-point surge in the share of Americans who support more firearms restrictions – a finding supported, though less dramatically, by a Pew Research poll conducted after the Newtown shootings.

That shift invigorated efforts to toughen restrictions on firearms.

For example, a visibly moved President Obama launched his new White House initiative, led by Vice President Joe Biden, to return with recommendations, and Sen. Dianne Feinstein (D) of California has said she will file a bill on Jan. 22 that, if passed, would reinstate an assault-weapons ban and force American gun owners to register "grandfathered" weapons with federal authorities.

"There are numerous efforts under way with an outside strategy, that is going to help capture this energy so it becomes more uncomfortable for Republicans not to move something,” an aide to a pro-gun-control lawmaker said on Monday, according to MSNBC.com

But while the gun-control movement has momentum and is urging Congress to strike quickly, new groups like the one started by Giffords may struggle to change the bedrock support in America for gun ownership.

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Yes, recent shootings "dramatize the problem, and people want a solution immediately," says Professor Goss at Duke.

But she also notes that recent poll numbers sliding toward more support for gun control "reflect this idea that, yeah, it's too easy for guns to get into bad hands, but [polls also show] that this is also a problem on a personal and family and cultural level. People are smart and they realize that, like a plane crash, there's never just one factor."