Omar Jadwat, the director of the ACLU’s Immigrants’ Rights Project, represented the plaintiffs in the arguments. He frustrated some of the court’s judges at first by not giving clear answers on whether the order was facially legitimate, which could allow it to survive under the Mandel standard. But he later broadly rejected the idea that Trump’s order should be upheld on such a low judicial threshold. “Deference cannot be a license to violate the Establishment Clause,” he told the judges, referring to the First Amendment clause restricting the state’s ability to institutionalize religion.

The case challenged the president’s second iteration of the executive order, which temporarily barred visa travel from six Muslim-majority countries for 90 days and suspended the U.S. Refugee Assistance Program for 120 days. The order constituted a revision of a January 27 directive that banned travel from seven total countries, permanently banned Syrian refugees, and included an exemption for religious minorities. That order’s sudden implementation on a Friday night led to chaos at major American airports as foreign travelers permitted to enter the United States upon takeoff were blocked by the time they touched down.

After a three-judge panel in the Ninth Circuit Court of Appeals upheld a nationwide injunction blocking the order in February, the Trump administration backed down and issued a more narrowly tailored version in March. But the second version has still struggled in the courts. Judge Theodore Chuang, a federal district-court judge in Maryland, issued a preliminary injunction blocking its enforcement a few hours after it was supposed to go into effect on March 16. Justice Department lawyers had argued that the March order’s revisions addressed concerns by multiple federal courts about the first order’s scope and constitutionality.

Chuang ruled against them, citing public comments by White House Press Secretary Sean Spicer, who said that “the principles of the [second] executive order remain the same” as the first, and former New York City Mayor Rudy Giuliani, who told Fox News that Trump had asked him for help on how to create a Muslim ban that would pass legal muster.

“The second executive order does not explain specifically why this extraordinary, unprecedented action is the necessary response to the existing risks,” he wrote. “But while the travel ban bears no resemblance to any response to a national-security risk in recent history, it bears a clear resemblance to the precise action that President Trump described as effectuating his Muslim ban.”

A Justice Department appeal challenging Chuang’s injunction would typically be heard by a three-judge panel in the Fourth Circuit. But the circuit’s judges voted last month to hear the case in an en banc panel, a rare procedural maneuver that places the case for consideration before the court’s full 15-judge bench. (Thirteen of the judges heard the case on Monday after two of their colleagues recused themselves.)