WASHINGTON — The Supreme Court for the first time Wednesday considers a major initiative of the Trump administration, reviewing whether President Donald Trump’s travel ban is a necessary step to protect the country from terrorism or an illegal and unconstitutional fulfillment of campaign promises to ban Muslim immigrants.

Lower courts have struck down each of the three iterations of the president’s proclamation, the first of which was issued just a week after he took office in January 2017. But the conservative-leaning Supreme Court may be Trump’s best hope, and it gave the administration a boost by allowing the ban to go into effect in December while considering the challenges to it.

The court will consider the third iteration of Trump’s travel ban, issued last fall, which barred various travelers from eight countries, six of them with Muslim majorities. They are Syria, Libya, Iran, Yemen, Chad, Somalia, North Korea and Venezuela. But restrictions on North Korea and Venezuela are not part of the challenge, and Chad was removed from the list earlier this month.

In requesting the court provide a final answer on the travel ban, Solicitor General Noel J. Francisco said the high court must reestablish the vast authority the president wields when the nation’s security is at stake.

“The courts below have overridden the President’s judgments on sensitive matters of national security and foreign relations, and severely restricted the ability of this and future Presidents to protect the nation,” Francisco wrote in his petition to the court.

The challengers are led by the state of Hawaii, who said its residents and educational institutions have suffered because of the ban.

Its lawyer, former Obama administration acting solicitor general Neal K. Katyal, told the court that Congress gives the president great power in immigration decisions, but not as much as he claims.

If so, Katyal wrote, “it would effect a constitutionally suspect delegation of authority, tantamount to granting the President a line-item veto over the entire immigration code. This court’s precedents bar Congress from vesting such extravagant and unilateral authority in the President.”

The immigration statute is enough for the court to strike down the ban, he said. But the proclamation also discriminates against travelers because of their religion, which violates the Constitution, Katyal wrote.

“A litany of statements by the President and his administration … plainly announce the President’s aim of blocking Muslim entry,” the brief states. “No principle justifies shutting the court’s eyes to this wealth of evidence.”

The justices are reviewing a unanimous ruling from a three-judge panel of the U.S. Court of Appeals for the 9th Circuit in San Francisco. That panel said the third version of the travel ban suffered from the deficiencies of the first two – that Trump had again exceeded his lawful authority and that he had not made a legally sufficient finding that entry of those blocked would be “detrimental to the interests of the United States.”

The U.S. Court of Appeals for the 4th Circuit struck down the ban on the constitutional question. The 9-to-4 decision took a deep dive into Trump’s statements and tweets since he became president and concluded the proclamation, like the first two, was motivated not by national security concerns but by antipathy toward Muslims.

However, Judge William B. Traxler Jr. switched sides, saying the administration’s work between the second travel ban and the third cured its problems for him.

The third version must be judged on the basis of the “context of the investigation and analysis that the agencies acting on the president’s behalf have completed, the consultation that has taken place between the president and his advisers, and the logical conclusions and rationale for the proclamation that are documented therein.”

Francisco told the court the third version was the result of a painstaking review process to determine which countries did not have procedures in place to screen out those who might intend to harm the United States.

The eight countries named in the current ban “do not share adequate information with the United States to assess the risks their nationals pose, or they present other heightened risk factors,” Francisco wrote. “Whereas prior orders of the President were designed to facilitate the review, the [current] Proclamation directly responds to the completed review and its specific findings of deficiencies in particular countries.”

The case is Trump v. Hawaii.

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