The National Rifle Association’s convention in Houston this weekend bristled with the combative and triumphant rhetoric of a group that achieved a major victory in 2013: completely defeating the White House-backed package of gun-control legislation.

On the surface, the gun-rights group seems stronger than ever with tens of thousands enthusiastic participants, record high membership and effusive approval for the path taken by the its leader, Wayne LaPierre.

Beneath the surface, however, some of the NRA’s allies are uneasy, saying publicly and privately that the organization is facing long-term — and even short-term — challenges on a scale it has not faced before.

Those challenges include changing demographics and patterns of gun ownership; a new willingness of gun-state lawmakers, particularly Democrats, to buck the NRA; and the rise of an organized and well-funded gun-control movement.

The concerns are playing out in a debate over whether the NRA and gun-rights advocates made a mistake by pugnaciously opposing all of this year’s major gun-control proposals — including legislation expanding background checks for gun purchases sponsored by two NRA-backed senators, Joe Manchin III (D-W.Va.) and Patrick J. Toomey (R-Pa.). That measure failed in a high-profile vote last month.

In recent days, one of the country’s best-known gun-rights advocates, Robert Levy, criticized the gun lobby for strenuously blocking the background check initiative on Capitol Hill. Levy, who was part of the legal team that won recent landmark gun-rights cases, also chairs the Cato Institute, an influential libertarian think tank that advocates for Second Amendment rights.

“The stonewalling of the background check proposal was a mistake, both politically and substantively,” Levy said recently, noting that public opinion favors such an approach. In an interview and in online blogs, Levy called for improvements in the legislation but noted overall that the Manchin-Toomey effort is “far better than the legal regime we now have.”

Levy has disagreed with NRA strategy in the past. But his views have been reinforced by others in recent weeks, most significantly by the votes of NRA-backed lawmakers who felt free to break with the gun lobby and support the background check proposal, particularly Democrats such as Jon Tester of Montana.

Pennsylvania may provide the most stark example of a reason for NRA worry. The state has one of the highest concentrations of NRA members in the country. Yet both senators — Toomey and Democrat Robert P. Casey Jr. — agreed to cross the NRA this year on its most high-profile vote of the year. In addition, three GOP House members from Pennsylvania, endorsed in the past by the NRA, have indicated support for the senators’ approach.

Still, NRA board member Grover Norquist says that NRA officials are thrilled with the results the NRA achieved this year on the state and national levels — accomplished despite the full-court press by the Obama White House and its gun-control allies.

A new report to be released this week by the Center for American Progress (CAP), a think tank with ties to the White House and the Democratic Party, looked into changes in Pennsylvania, Virginia and Colorado, citing gains there resulting in part from the grass-roots efforts of gun-control forces.

For example, since 2008, New York Mayor Michael R. Bloomberg (I) and the organization he founded and funds, Mayors Against Illegal Guns, has been active in the state, building a coalition of more than 150 mayors. Bloomberg’s organization also has been at work in other traditional gun states, such as Colorado and Virginia, where senators also supported the Manchin-Toomey background check proposal last month.

The support of purple-state senators for legislation that the NRA strongly opposes is not in itself an indicator of change. Members in the past have bucked the NRA, and some of them found themselves facing early retirement.

This time may be different, however, in part because of the demographic trends that seem to be running against the gun rights group. As the country becomes more suburbanized, gun culture is diminishing in popularity and influence and the gun-control movement’s support is increasing.

The CAP report, for example, notes that “while the number of guns in circulation in the country has continued to rise, the percentage of households that own guns has been steadily declining for the past three decades — reaching a low of 34 percent in 2012, down from an average of 50 percent in the 1970s.”

Perhaps most worrisome for the NRA is the flow of funds from Bloomberg to groups that are trying to take a page from the NRA playbook. The NRA remains one of the most potent political forces in American politics today because its members feel passionately about gun rights, and their passion is reflected in real political participation. But the “intensity gap” is closing, the CAP said.

“There is substantial evidence that the intensity gap has closed,” wrote the report’s author, Arkadi Gerney, who worked previously with the mayors’ group. He cited a Fox News poll conducted the day after the Toomey-Manchin vote, which “showed that three times as many Americans said that they were likely to support a candidate who voted for expanded background checks (68 percent) as a candidate who opposed expanded background checks (23 percent).” They also cited the example of Sen. Kelly Ayotte (R-N.H.), who saw her approval drop since the vote and who has been dogged by gun-control advocates during a recent Senate recess.

NRA board members are aware of these new pressures, of course. Do they have regrets about the way the organization handled the background check issue with a defiant, oppositional post-Sandy Hook stance?

“None whatsoever,” said Cleta Mitchell, a board member who has served as outside counsel to the NRA in the past. “The NRA stands as a stalwart, as being true to principles and not caving.” The NRA has called for more armed guards in schools and greater attention to mental health issues and the role of violent video games and other entertainment.

Mitchell said she has concerns about the affects of Bloomberg’s spending, among them the hypocrisy of complaining by the White House and its allies on the left. “The president has the nerve to say the Senate vote outcome was due to ‘special interests.’ Why are the votes against the Second Amendment ‘principled’ and the votes on our side are ‘political?’ ” she asked.

The dedication of NRA members to protecting Second Amendment rights is an important asset for the group. Both sides in the debate over expanding background checks say the power of the NRA and the issue it champions will be visibly tested during the 2014 election campaign.

“We are in the midst of a once-in-a-generation fight for everything we care about,” LaPierre told the convention this weekend. The convention’s motto was “Stand and fight.”

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