But, but, the NRA seems to be saying that you can easily build a gun registry simply using the phone metadata. If what you say is true, then not all people that call the NRA have a gun !!! Next thing you know, you'll tell me some people have guns and never call the NRA.
Then you don't understand the argument.
It's not just the NRA, it's gun stores, gun clubs, gun ranges and other gun owners. If you were to take a look at everyone who called a gun store, gun club, target range and known gun collectors over the past 5 years, you'd have a pretty good idea of who owns guns in the country. That's the creation of a backdoor registry and since creation of a registry is already forbidden under federal law, the NRA's point is a salient one.
The NSA can retain metadata until the political winds shift enough to allow the creation of such a registry.