“Federal courts,” the brief said, “have no more sacred role than protecting marginalized groups against irrational, discriminatory conduct.”

In the Ninth Circuit, the Trump administration said judges were ill-equipped to decide cases involving national security. “Unlike the president,” the administration’s brief said, “courts do not have access to classified information about the threat posed by terrorist organizations operating in particular nations, the efforts of those organizations to infiltrate the United States, or gaps in the vetting process.”

Noah G. Purcell, the solicitor general of Washington State, appeared to concede in court that there were areas in which Mr. Trump was entitled to act. But he asked the court to protect people whose lives had been changed by Mr. Trump’s order in a flash.

“The focus of our claim,” he said, “is on people who have been here and have, overnight, lost the right to travel, lost the right to visit their families, lost the right to go perform research, lost the right to go speak at conferences around the world. And also people who had lived here for a long time and happened to be overseas at the time of this order, which came with no warning whatsoever, and suddenly lost the right to return to the United States.”

How much power has Congress given the president?

On Friday, defending Mr. Trump’s executive order in a Seattle courtroom, Michelle Bennett, a Justice Department lawyer, cited Youngstown Sheet & Tube Co. v. Sawyer, a 1952 decision in which the Supreme Court rejected President Harry S. Truman’s assertion that he had the authority to seize steel mills during the Korean War.

The most famous part of the decision is a concurrence from Justice Robert H. Jackson, which set out a framework for considering clashes between presidential power and congressional authority. The president has the most power when he acts with congressional authorization, Justice Jackson said, and an intermediate amount when Congress is silent. The president’s power is at its “lowest ebb,” Justice Jackson wrote, when Congress has forbidden a particular action.

Truman’s actions fell into the third category, Justice Jackson wrote. Ms. Bennett, by contrast, said Mr. Trump’s order was in the first category.