A federal appeals court shaped by Trump is at the center of a debate over border authority.

The 13 federal appeals courts spread across the country sit just below the U.S. Supreme Court. In theory, the appeals courts, each covering a judicial circuit, are equals. But often enough in American history, one circuit court takes on an outsize role in shaping seminal constitutional questions that end up before the Supreme Court.

At the moment, that judicial limelight belongs to the U.S. Court of Appeals for the Fifth Circuit, which is weighing the fate of a Texas law that would give police officers in the state the power to arrest people suspected of having entered the U.S. unlawfully — a power that has long been understood to rest with the federal government.

It is a case with far-reaching legal and political implications, and it has thrust the Fifth Circuit into the middle of a fierce debate over the extent of federal power over the nation’s borders.

Based in New Orleans, the Fifth Circuit hears cases from three states — Texas, Mississippi and Louisiana — and the composition of the court was dramatically shaped by President Trump, who nominated six of the 17 judges. Six of the others were nominated by other Republican presidents.

Over the past few years, the Fifth Circuit has developed a reputation for muscular conservatism. Many of its judges adhere to “originalism,” which seeks to interpret the Constitution through the lens of its 18th-century authors.

That has led the Fifth Circuit to stake out some positions — such as protecting a violent abuser’s legal access to firearms — that even the Supreme Court’s conservative majority has appeared skeptical of. In the nine decisions from the Fifth Circuit that were reviewed by the Supreme Court last term, seven were reversed.

Even so, the Fifth Circuit’s growing role in teeing up Supreme Court cases is unmistakable. The number of cases from the Fifth Circuit that were taken up by the nation’s highest court more than tripled during the Trump administration. And the fact that it handles appeals from the federal district courts in Texas means the Fifth Circuit is likely to stay very busy, as the state’s governor and attorney general continue to mount legal challenges to federal authority over immigration and the border.