In 2011, the ATF began requiring dealers in Southwestern border states to report sales of multiple semiautomatic rifles to individual purchasers. The ATF doesn't have the authority to do this.* As such, the requirement has been challenged in the DC and 5th Circuit courts, but it was upheld in both instances.
Today, the 10th Circuit issued a ruling [pdf] affirming them.
Among the lovely chestnuts of wisdom was this:
A review of Project Gunrunner conducted by the Office of the Inspector General (“OIG”) indicates that tracing guns seized in Mexico can provide “crucial” information in gun-trafficking investigations and generate intelligence regarding trends in gun smuggling. (…) [Assistant Director of Field Operations William Hoover] explained that trace information helps ATF “reconstruct the flow of weapons along the border, how and where they are being purchased, and who is purchasing them.”
Yeah, because that worked so well when Project Gunrunner was active.
* Here's the multiple-handgun form [pdf]. It specifies "pistol or revolver." Nowhere does it grant them the power to demand reporting of long guns. If they want that, they have to get authority from Congress.