AR-15s are typically possessed by law-abiding citizens for lawful purposes—including self-defense, which the Supreme Court has called “the core lawful purpose”—and so are protected under the Second Amendment. That provision also guarantees the right to keep and bear certain arms for another key purpose: “the security of a free State.” AR-15s help secure both the individual and the system of constitutional liberty.

These cases, which the Supreme Court has accepted for review, challenge Cook County, Illinois’s and Connecticut’s bans on AR-15s. Americans possess an estimated 20 to 30 million AR-15s, using them for self-defense, sporting, and hunting. AR-15s are “in common use” for lawful purposes and so protected by the Second Amendment.

Determining what the Supreme Court meant by the term “common use” has proven difficult for lower courts. Several decisions have split hairs as to AR-15s’ usefulness for self-defense as compared with other potential uses and lawful weapons. This approach wrongly assumes the Court has “severed” the link between the militia and Second Amendment protection. Cato filed an amicus brief urging the Court to clarify that a “non-militaristic limitation” is atextual and ahistorical. The Constitution protects AR-15s because they are suited to self-defense and the militia.