Gun-rights advocates appear to be on the brink of killing a renewed assault weapons ban on Capitol Hill. But the movement's post-Newtown victory is hardly complete — and success may be a high water mark in the political unity of gun proponents.

RELATED: How the NRA Uses Women as Human Shields

The ban on assault weapons championed by Senator Dianne Feinstein of California was never the most popular or easiest component of a Democratic push for tighter gun rules. Last week, it passed out of the Democratically controlled Senate Judiciary Committee on a straight party-line vote. Now, Politico reports that Senate Majority Leader Harry Reid will not include the bill in the package that comes to the Senate floor. Instead, it would likely be added as an amendment to a package that includes two or three of the other Senate proposals: tighter laws on gun trafficking, more funding for school safety, and background checks. The first two measures are seen as more likely to pass; offering the assault weapons ban as an amendment means it would require its own vote — which would almost certainly fail.

RELATED: What Happens When an A-Rated GOP Senator Turns His Back on the NRA?

Since the original assault weapons ban expired in 2004, support for such a measure has waned, as shown below. That Feinstein's proposal includes weapons like the AR-15 (which has become enormously popular since the ban expired), the revamped proposal faced political uncertainty even if the National Rifle Association hadn't gotten involved. Data from Gallup

RELATED: Wayne LaPierre Will Testify Before Congress

But the NRA did get involved, quite literally. The organization's Get Involved page encourages visitors to write to their representatives to express outrage at Feinstein's "egregious" proposal. In a sign of how confident the organization felt that Feinstein's proposal would fail, her bill is used in the sample letter to demean all other proposed gun laws.

RELATED: Wayne LaPierre Only Said What Gun Nuts Have Been Posting on Facebook

Story continues

As we've noted before, this is a significant change of fortune from the days immediately following the Newtown massacre, when gun stocks plummeted, the NRA sat silent, and legislators spoke about renewing the ban. In fact the says since Newtown have been highly lucrative for gun manufacturers, as the threat of curtailed availability prompted a run on weapons of all kinds.

RELATED: NRA Snubs Obama

Over the years, gun manufacturers have learned to let the NRA lead on political issues, as Businessweek reported last week — and so far, that strategy has worked. The organization is primarily funded by individual members, and is largely responsive to that group. But it's also pushed farther to the right by other gun groups.

Smaller, even more confrontational groups jostle with the NRA for attention and give LaPierre heartburn, say people who have worked with him over the years. Gun Owners of America, for example, calls itself “the only no-compromise gun lobby in Washington,” an unsubtle dig at the NRA. Two days after the elementary school massacre, Larry Pratt, leader of the Springfield (Va.)-based GOA, jumped in front of LaPierre with a blistering op-ed in USA Today: “In addition to the gunman, blood is on the hands of members of Congress and the Connecticut legislators who voted to ban guns from all schools in Connecticut. They are the ones who made it illegal to defend oneself with a gun in a school.” Pratt’s group says it has 300,000 members; the NRA claimed 4 million before Newtown and says it has added hundreds of thousands since.

Indeed, the NRA's success in repelling unwanted post-Newtown laws has been impressive. Its ability to maintain dominance over competitors has been without flaw. When gun rights are threatened, the NRA is the go-to brand, the way CNN sees its viewership spike during live news events.

The bigger threat, then, may not be from Gun Owners of America. It may be from gun owners of America.

We've reported on Defense Distributed a number of times before, a group which aims to offer 3D-printable weapons components for free online. The group already has a search engine available, including plans for a lower receiver and grip for an AR-15. The roadblock to a world in which any American can print the pieces to a semi-automatic weapon is only access to a 3D printer. Meaning that the only roadblock to broadly distributed, hard-to-regulate gun ownership is a piece of technology that, over time, will almost certainly become commonplace.

The NRA hasn't officially responded to the work of Defense Distributed, though the organization's Cody Wilson isn't expecting a warm embrace.

Wilson also believes that his frequent usage of the term “anarchist” is what prevented what he calls “Red Staters” from throwing their support behind Defense Distributed.

"For a long time, early on, NRA types didn't like us because they saw what we were doing and were afraid that it would only mean more regulation.”

Which it may. But the NRA has another reason to fear "anarchists" — Defense Distributed could create an anarchic gun rights movement, undermining the overarching brand of the NRA.

Over the weekend, Defense Distributed's Facebook page displayed the organization's newest acquisition: a license from the Bureau of Alcohol, Tobacco, and Firearms to manufacture and sell weapons. What this means for the organization's plans to distribute free 3D models of components online, time will tell. But it moves the group into a new point of tension with gun manufacturers and the NRA. Why buy an AR-15 from Bushmaster when you can buy most of the parts for far less and assemble it yourself? Or, farther in the future: Why donate to the NRA every month when you have access to any weapon you could want, on demand?

Feinstein's proposed assault weapons ban mirrors the one passed in 1994 and which expired a decade later. Another decade on, the debate has shifted beyond what was once recognizable. The defeat of Feinstein's bill may end up being a bookend to a political era, one dominated by gun rights advocates that were unprepared for how the world was about to change.