“WELCOME NRA” read the signs in the windows of every bar in downtown Nashville. The National Rifle Association has taken over the town for its annual conference—a deadly ComicCon of sorts that boasts “9 acres of guns!”—and joining them soon will be the entire field of likely Republican primary contenders, who will flood the stage of the Music City Center on Friday to fight over the affections of the pro-gun constituency.

The entire field, that is, except for Rand Paul, who was not invited.

Publicly, the NRA’s relationship with Paul is cordial, but he maintains ties to 2nd Amendment organizations, run by or involving longtime allies of his father, that are openly hostile toward the NRA. They are ties, the NRA knows, that he may never break.

“I can confirm that we did not extend an invitation,” Jennifer Blake, the NRA’s spokeswoman, told me by phone Wednesday. But, she said, it was Paul’s own fault because his campaign hadn’t requested an invitation. “They did not reach out to us,” she said.

Had they reached out, I asked, would he have been invited? “I can’t say definitively that we would have,” she said. “But I can say he was not issued an invitation.”

However, a source with knowledge of Paul’s dealings with the NRA said the claim that he did not request an invitation to the convention was “not true.”

Further, the source said, “Is that really how invitations work?”

Paul has an A-rating from the NRA, but the objective grading of his gun-rights credentials has little to do with the politics of the pro-gun lobby, wherein his involvement with extremist groups tied to his father, former congressman and libertarian-icon Ron Paul, has not won him many friends.

“Sometimes the NRA doesn’t like it when people are bigger defenders of the issue than they are,” the source suggested. “They also don’t like it that he helps other, stronger groups like the Gun Owners of America and the National Association for Gun Rights.”

The Gun Owners of America was founded in 1975 by a former member of the NRA board of directors, H.L. Richardson, and makes a sport out of publicly criticizing the NRA.

In the aftermath of the Sandy Hook Elementary School mass-murder in 2012, the GOA said its rival was hiding from the media: “Whenever there’s a tragedy, they go into possum mode,” chief counsel Mike Hammond told The Huffington Post. “They think that if they don’t say anything that it will go away.”

Prominently displayed on the GOA website homepage is a testimony from Ron Paul, who has an A+ rating with the group. He calls them “The only no-compromise gun lobby in Washington.”

Dennis Fusaro, an aide to the elder Paul during his presidential campaigns, previously served as the GOA’s director of state legislation. (Fusaro is no longer a friend to the Pauls, having taped and leaked the conversations that broke open the Kent Sorenson scandal.)

The National Association for Gun Rights, established in 2000 by Dudley Brown, defines itself as a far-right NRA. Brown made a name for himself when, after the Newtown and Aurora mass murders resulted in new gun-control laws in his home state of Colorado, he told NPR: “There’s a time to hunt deer, and the next election is the time to hunt Democrats.”

According to Buzzfeed’s Rosie Gray and Kate Nocera, Brown says he “supported the elder Paul’s 2012 presidential bid” and has known Doug Stafford, a longtime member of the inner circle of both Pauls and currently Rand Paul’s main political adviser, “for years.”

On the NAGR’s board of directors sits Michael Rothfield, the founder of Saber Communications, a political consulting firm based in Virginia. Rothfield was paid $7.7 million for his work on the elder Paul’s 2012 presidential campaign. And, as David Weigel extensively reported, Rothfield mastered the direct-mail system that ultimately vaulted Paul into the Senate.

In September in Virginia, the NAGR provided a large assault weapon to the Liberty Political Action Conference, hosted by the Campaign for Liberty, of which Ron Paul is chairman. The weapon sat on a table underneath a large poster featuring Rand Paul’s face and a quote from him declaring “I’m a member.” Passersby were tempted to, as one ponytailed man did, point the weapon at a placard stamped with President Obama’s face.

Richard Feldman, a former NRA lobbyist and author of Confessions of a Gun Lobbyist, told me on Wednesday that he was “very surprised” by the NRA’s decision to snub Paul. “I’m surprised the NRA would play this game with a serious candidate who is pro-gun.”

But, Feldman said, Paul’s history with fringe gun groups “would explain” the NRA’s games “better than anything on a policy level…He’s in the same space on guns as a Huckabee, a Santorum, or a Walker.”

One way to look at the NRA's decision is that they are—however passive aggressively—challenging Paul. The GOA and the NAGR believe not merely that they are more conservative than the NRA, but that they are better and stronger at what they do because of it. The NRA, which Paul’s camp considers to be “the establishment,” seems to be tempting Paul to put those assertions to the test in the Republican primary.

And in a way that’s a metaphor for Paul’s campaign itself.