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.