25 APR 2018: The US Supreme Court is saving one of its biggest cases for last. The justices are hearing arguments today over Donald Trump’s ban on travellers from several mostly Muslim countries. It’s the last case the justices will hear until October.

The Trump administration is asking the court to reverse lower court rulings striking down the ban. The policy has been fully in effect since December, but this is the first time the justices are considering whether it violates immigration law or the Constitution.

The court will consider whether the president can indefinitely keep people out of the country based on nationality. It will also look at whether the policy is aimed at excluding Muslims from the United States.

People have been waiting in line for a seat for days. In another sign of heightened public interest, the court is taking the rare step of making an audio recording of the proceedings available just hours after the arguments end. The last time this was done was for the gay marriage arguments in 2015.

The travel ban is the first Trump policy to undergo a full-blown Supreme Court review. The justices are looking at the third version of a policy that Trump first rolled out a week after taking office, triggering chaos and protests across the US as travellers 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 The first version was blocked by courts and withdrawn.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 travellers from five countries with overwhelmingly Muslim populations – Iran, Libya, Somalia, Syria and Yemen. It also affects two non-Muslim countries: blocking travellers from North Korea and some Venezuelan government officials and their families. A sixth majority Muslim country, Chad, was removed from the list this month after improving “its identity-management and information sharing practices,” Trump said in a proclamation.

Trump’s campaign pledge to shut down Muslim entry into the US, his presidential tweets about the travel ban and last fall’s retweets of inflammatory videos that stoked anti-Islam sentiment all could feature in the justices’ questioning of Solicitor General Noel Francisco, defending the ban, and Neal Katyal, the former acting solicitor general under President Barack Obama. Katyal is representing the challengers.

The administration has 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. Francisco also has said in written arguments that Trump’s September proclamation laying out the current policy comports with immigration law and does not violate the Constitution because it does not single out Muslims.

The challengers, backed by a diverse array of supporting legal briefs, have said that Trump is flouting immigration law by trying to keep more than 150 million people, the vast majority of them Muslim, from entering the country. They also argue that it amounts to the Muslim ban that Trump called for as a candidate, violating the Constitution’s prohibition against religious bias.

A decision in Trump v. Hawaii, 17-965, is expected by late June.