In April, Mr. Trump appeared likely to win his argument, when the case was heard by the high court in April. Chief Justice John Roberts and Justice Anthony Kennedy both signaled support for the travel policy in arguments. The ban's challengers almost certainly needed one of those two justices in order to strike down the ban on travelers from several mostly Muslim countries.
The justices voted in December to allow the policy to take full effect pending their full consideration.
The Trump administration asked the court to reverse lower court rulings that would strike down the ban.
The Supreme Court also considered whether the president can indefinitely keep people out of the country based on nationality, and it also looked at whether the policy is aimed at excluding Muslims from the United States.
Kennedy challenged lawyer Neal Katyal, representing the challengers, about whether the ban would be unending. He said the policy's call for a report every six months "indicates there'll be a reassessment" from time to time.
The travel ban was the first Trump policy to undergo a full-blown Supreme Court review. The justices examined the third version of a policy that Mr. Trump first rolled out a week after taking office, triggering chaos and protests across the U.S. as travelers were stopped from boarding international flights and detained at airports for hours. The first version was blocked by courts and withdrawn. Its replacement was allowed to take partial effect, but expired in September.
The current version is indefinite and now applies to travelers from five countries with overwhelmingly Muslim populations — Iran, Libya, Somalia, Syria and Yemen. It also affects two non-Muslim countries, blocking travelers from North Korea and some Venezuelan government officials and their families. A sixth majority-Muslim country, Chad, was removed from the list in April after improving "its identity-management and information sharing practices," Mr. Trump said in a proclamation.
The administration argued that courts have no role to play because the president has broad powers over immigration and national security, and foreigners have no right to enter the country.
The challengers argued that his policy amounts to the Muslim ban that Mr. Trump called for as a candidate, violating the Constitution's prohibition against religious bias.
