President Donald Trump's revised immigration ban faced the first of several challenges in court Wednesday, one day before it was due to take effect.

Here are key points of the overhauled executive order.

What's in it?

Iraq, which was targeted by the original Jan 27 travel ban, is excluded this time. Six other countries remain: Syria, Libya, Somalia, Yemen, Sudan, and Iran. The US says that none of the six can supply adequate identity and security information on their citizens to satisfy US needs to safely vet visa applicants.

People with pre-existing, valid visas from the six countries are explicitly exempted from the restrictions in the new order, as are permanent US residents ─ so-called green card holders. The original ban had extended to people with valid visas and even those with permanent residency, causing havoc at airport arrival halls and sparking a large number of legal challenges.

Why a revised order?

A Washington state judge halted implementation of the original order on Feb 3, accepting legal challenges that said it violated the constitutional rights of immigrants and their families by specifically targeting Muslims. The judge was supported by an appeals court, forcing the Trump administration to redraft the order.

How long does the new order last?

Ninety days from its implementation date for the six countries on the list. The aim is to give them time to improve their databases and screening systems to boost US confidence in the visa issuance process. But officials said there is no guarantee that the ban will be lifted after 90 days. It depends on how well the countries comply with US requirements.

What about refugees?

Trump's new order places a 120-day ban on refugee arrivals from any country. Officials say they need to strengthen vetting procedures for refugees to prevent potential terrorists from entering the country. They said that the Federal Bureau of Investigation is currently investigating 300 refugees already inside the United States for suspected terror links or sympathies.

In the first order, refugees from war-torn Syria were banned indefinitely. But now they have the same status as other refugees.

At the same time, the order ─ like its predecessor ─ cuts the number of refugees the government will admit this year to 50,000, down from 110,000 originally envisaged.

Is this a ban on Muslim arrivals?

The US government rejects the notion, pointing out that visa issuance and arrivals remain unchanged from Muslim-majority countries like Saudi Arabia, Indonesia, Pakistan, as well as those in North Africa.

But critics continue to point to Trump and other administration official statements made during and after last year's presidential campaign to argue that the intention has always been to screen out Muslim arrivals.

"The Trump administration has conceded that its original Muslim ban was indefensible. Unfortunately, it has replaced it with a scaled-back version that shares the same fatal flaws," said Omar Jadwat, director of the American Civil Liberties Union's Immigrant Rights Project.