A rift is emerging among the Supreme Court’s conservatives — and it could thwart the court’s recent march to expand gun rights.

On one side is the court’s oldest and most conservative justice, Clarence Thomas. On the other is its youngest member, Amy Coney Barrett.

The question at the center of the spat may seem abstract: How should the court use “history and tradition” to decide modern-day legal issues? But the answer may determine how the court resolves some of the biggest cases set to be released in the coming days, particularly its latest foray into the Second Amendment right to bear arms.

If the court adheres to a strict history-centric approach, as Thomas favors, it will likely strike down a federal law denying firearms to people under domestic violence restraining orders.

But Barrett recently foreshadowed that she is distancing herself from that approach. If she breaks with Thomas in the gun case, known as United States v. Rahimi, and if she can persuade at least one other conservative justice to join her, they could align with the court’s three liberals to uphold the gun control law.