A federal judge heard arguments Monday on the constitutionality of a Colorado law requiring gun buyers to wait three days after a background check is initiated before taking possession of a firearm. The 2023 law generally imposes a three-day waiting period on firearm purchases after the initiation of a background check.

Attorneys for the law's challengers argued the policy has no grounding in the nation's founding-era legal traditions. "The first 'cooling off'-style waiting period did not come into existence until the 1990s. Thirty years ago. Hardly a tradition," said attorney Michael D. McCoy for the law's challengers. McCoy contended the outcome was already determined by recent appellate rulings. "How does Colorado's firearms waiting period law now survive?" he said. "It doesn't. It simply can't."

The state pushed back, arguing Colorado's approach is meaningfully distinct from laws already struck down in the circuit. Representing the state, Assistant Solicitor General Joseph G. Michaels argued that while Colorado was also concerned about reducing gun homicides and suicides, its three-day waiting period coincided with the window in federal law for the processing of background checks. "Whether it's under a federal background check or whether it's under Colorado's waiting period law, three days is constitutionally acceptable," Michaels said.

The case sits at the intersection of two competing appellate precedents that the presiding judge flagged as a threshold problem. In 2024, a three-judge panel of the U.S. Court of Appeals for the 10th Circuit issued a precedent-setting opinion in Rocky Mountain Gun Owners v. Polis, in which challengers sought an injunction against Colorado legislation raising the gun purchasing age from 18 to 21; the panel rejected the challengers' request. In that decision, the majority concluded that an age-related condition on gun purchases did not fall under the Second Amendment's "keep and bear arms" guarantee, pointing to a 2008 Supreme Court decision that cautioned nothing in that opinion should cast doubt on "laws imposing conditions and qualifications on the commercial sale of arms."

A separate 10th Circuit panel subsequently reached a different conclusion when examining a New Mexico waiting period law. By a 2-1 vote, the majority in Ortega v. Lujan Grisham disagreed that a waiting period was a "condition and qualification" on commercial gun sales that fell outside the Second Amendment, and in its own precedent-setting decision found New Mexico's waiting period law to be likely unconstitutional. New Mexico, with support from Colorado, asked the 10th Circuit to invoke a procedural tool allowing the entire court to reconsider the case, but by a 10-2 vote the full-time judges declined.

U.S. District Court Senior Judge John L. Kane, who is presiding over the Colorado case, had already signaled concern about the Supreme Court's historical framework for Second Amendment challenges. "I previously expressed my concern that such an independent analysis could lead to inconsistent holdings, as the parties could craft distinct records and present varying arguments in different cases," Kane wrote. Kane instructed the parties before the hearing to address the potential problem the 10th Circuit created with dueling precedents on the subject of gun purchases.

Kane will issue a written decision. Whether that ruling will be appealed — and how the 10th Circuit would resolve the tension between its two conflicting precedents — remains to be seen.