WASHINGTON — President Trump’s executive order on immigration has prompted a constitutional showdown that could leave a mark on the law for generations and seem

WASHINGTON — President Trump’s executive order on immigration has prompted a constitutional showdown that could leave a mark on the law for generations and seems likely to end in a landmark Supreme Court decision. A ruling by the court on Mr. Trump’s travel ban on seven predominantly Muslim countries could help answer some crucial legal questions: How much independent constitutional authority does the president have over immigration, and how much power has Congress given him? The likely answer to both questions: a lot. But other parts of the Constitution may temper or defeat that power. Among them are the due process and equal protection clauses and the First Amendment’s ban on government establishment of religion. Here is a look at the leading arguments in the case. What have the judges said? Many trial judges around the country have blocked aspects of Mr. Trump’s executive order. But none have issued an order as broad as the one by Judge James Robart, a federal judge in Seattle, who blocked the key parts of the executive order, which had suspended travel from the seven countries and limited the nation’s refugee program. Continue reading the main story Related Coverage Trump Clashes Early With Courts, Portending Years of Legal Battles FEB. 5, 2017 Lifting of Travel Ban Sets Off Rush to Reach U.S. FEB. 5, 2017 Where Trump’s Travel Ban Stands FEB. 5, 2017 Trump Protesters Borrow From Tea Party to Put Pressure on Lawmakers FEB. 5, 2017 Advertisement Continue reading the main story The case is now before the United States Court of Appeals for the Ninth Circuit, in San Francisco. That court on Saturday declined to issue an immediate stay of Judge Robart’s order, but it indicated that it would weigh in soon after additional briefs were filed, with the last one due Monday afternoon. After it rules, an appeal to the Supreme Court seems likely. Judge Robart’s brisk ruling contained almost no reasoning. By contrast, Judge Nathaniel M. Gorton, of the Federal District Court in Boston, issued a 21-page decision on Friday refusing to block the program and discussing the legal arguments in detail. Judge Gorton also sketched out the broader picture. “The rich immigrant history of the United States has long been a source of strength and pride in this country,” Judge Gorton wrote. “Conversely, the public interest in safety and security in this ever-more dangerous world is strong as well.” The balance, he wrote, tipped in favor of Mr. Trump. How broad is the president’s constitutional power? Article II of the Constitution confers authority on the president, the Supreme Court has said, to conduct foreign affairs and address immigration. In their brief to Judge Robart, lawyers for Washington State, one of the two plaintiffs, along with the State of Minnesota, said there were constitutional checks on these powers. “While courts generally give more latitude to the political branches in the immigration context, this does not mean that the political branches can act with impunity,” the brief said. “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.”