The case Garland v. VanDerStok, concerning the legality of a Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) rule regulating firearm parts kits and partially complete receivers. The Solicitor General argued the rule is consistent with existing law and addresses a serious public safety issue, while the respondents contended the ATF exceeded its statutory authority by expanding the definition of "firearm." The justices questioned both sides extensively on the definitions of key terms within the Gun Control Act of 1968 and the appropriate standard of review for the rule. The core dispute centers on whether the ATF's interpretation of "readily convertible" is a permissible expansion of the law or an impermissible overreach.