US President Donald Trump is preparing to release an updated executive order tomorrow (Monday, US time), according to multiple reports.

The first order temporarily halted travel from citizens of seven Muslim-majority nations, which triggered nationwide protests and legal challenges.

But on February 9 it was struck down by the 9th Circuit federal appeals court, who argued the Government presented no evidence to explain the urgent need for the order to take effect immediately.

The new order, which was initially planned to be released last week, will seek to iron out some of the problems of the first travel ban.

Here's a breakdown of what we might expect.

So, what's changed?

Homeland Security Secretary John Kelly said the new executive order would be a "more streamlined version of the first [order]".

It will seek to prevent some of the doubt which occurred the first time around by ensuring "no one is caught in the system of moving from overseas to US airports", Mr Kelly said.

This is because the original travel ban temporarily blocked citizens of Syria, Sudan, Yemen, Iran, Iraq, Somalia and Libya from entering for 90 days — while some affected travellers were mid-air.

It also excluded all refugees for 120 days, except those from Syria, who were banned indefinitely.

But it caused a weekend of chaos at the nation's airports as customs officials were left confused about what it actually meant and which classes of travellers were included.

Sorry, this video has expired Trump says America should have had 'extreme vetting' for many years

Who will be affected?

The Washington Post and CNN have reported the order will not impose a blanket ban on those from Iraq.

Those reports follow pressure from the Pentagon, which had called on the White House to reconsider including Iraq from its ban because of the country's role in fighting Islamic State.

Who's affected by the travel ban? Firstly, Mr Trump signed the executive order on January 27

Firstly, Mr Trump signed the executive order on January 27 It barred travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen from entering the US for 90 days

It barred travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen from entering the US for 90 days It also stopped all refugees from entering the country for 120 days

It also stopped all refugees from entering the country for 120 days Except refugees from Syria — they've been banned indefinitely

Except refugees from Syria — they've been banned indefinitely Green-card holders had been stopped during the first weekend of the order. Since then, the White House has said those residents wouldn't be affected moving forward

It was originally thought that the order would still apply to citizens of all the countries originally named. This was based on assurances from senior White House policy adviser Stephen Miller, who told Fox News the revised order would still apply to the same countries.

According to sources in a separate CNN report, Mr Miller has been less involved in drafting the second order. That's allowed a greater role for the White House counsel and Republicans in Congress. (Another source in the same report said Mr Miller was more, not less, involved in this order.)

Will it solve the green card issue?

Mr Kelly said one of the key differences of the new order is that it will not prevent foreign nationals with either a work visa or green card permanent residency permit from re-entering the US.

Asked whether green card residency permit holders would be allowed in, Mr Kelly said: "It's a good assumption."

This could alleviate some concerns with the original order expressed by judges in the 9th Circuit court.

And what if you're mid-air when the order is signed?

Mr Kelly also said foreign travellers with visas who would already be in the air when the order takes place will not be affected either.

"As far as the visas go ... if they're in motion from some distant land to the United States, when they arrive they will be allowed in," he said.

Instead the aim is to ensure "that people on the other end don't get on aeroplanes".

After concerns were raised that not enough notice had been given to individuals prior to restricting their travel, Mr Kelly revealed this time there would be a "short phase-in period".

So what will be the same?

Mr Miller said a revised version of the travel ban would "have the same basic policy outcome".

Basically, the revised executive order will resolve "a lot of very technical issues that were brought up by the court", he said.

In rejecting the administration's first order, the 9th Circuit Court noted the compelling — and in this case competing — public interests of both sides.

"On the one hand, the public has a powerful interest in national security and in the ability of an elected president to enact policies," the court said at the time.

"And on the other, the public also has an interest in free flow of travel, in avoiding separation of families, and in freedom from discrimination."

It is unclear how else the administration plans to address these issues, with some experts warning that legal problems may remain if the only real change is to exempt green card holders.

And what can't change?

Part of the federal court challenge focused on some of Mr Trump's own comments as a presidential candidate in which he called for a "shutdown of Muslims entering the United States".

Those comments and others like them from Mr Trump's supporters remain on the public record and would form part of any challenge to a rewritten order.

The administration, however, also points to subsequent comments from the then-candidate that his policy was for "extreme vetting", not a ban on Muslims.

Why is this significant?

Mr Trump's first executive order, which followed through on one of his fundamental campaign promises, was problematic because of the mass confusion it created at airports around the country.

After it was quickly halted by federal courts, the administration's options were to appeal to the Supreme Court, rescind the order, or write a new order.

CNN has cited two sources saying they expect Mr Trump will formally revoke the earlier executive order.

The effectiveness of this new order will be seen as a reflection of the Trump administration's reputation — so there's not a lot of room to get it wrong.