President Trump's newest travel ban begins today

After months of winding through the courts, the so-called "watered down," revised version of President Donald Trump's fiercely litigated travel ban will finally go into effect at 8 p.m. ET Thursday.

Here's what to expect for version 2.0:

Who can't enter the U.S.?

The test for foreign nationals under the Supreme Court's ruling is whether one has a "credible claim of bona fide relationship" with either an entity (like a school or a job) or a person living in the US (such as a spouse).

If you can't sufficiently establish such a close relationship, you are banned for 90 days if you are from Libya, Syria, Iran, Somalia, Yemen and Sudan, and 120 days if you are a refugee from any country.

The new guidelines, sent to overseas posts on Wednesday, say that applicants must prove a relationship with a parent, spouse, son, daughter, son-in-law, daughter-in-law or sibling in the US, according to a senior administration official. They have not yet been posted by the State Department or the Department of Homeland Security and could be subject to change.

Advocacy groups such as Amnesty International plan to send researchers to US airports, such as Dulles International Airport and John F. Kennedy Airport on Thursday, to monitor developments and observe implementation of the ban in case any disputes arise.

Who is exempt from the ban?

Before the executive order was halted by the courts, the following categories of travelers were excluded from the travel ban (and are expected to remain exempt this time around):

-- US citizens -- Legal permanent residents (aka green card holders) -- Current visa holders -- Dual nationals -- Foreign nationals with "bona fide" family, educational or business ties to the US -- In addition, the executive order permits the issuance of a visa to, and entry of, someone who would otherwise be excluded on a case-by-case basis at the discretion of DHS and the State Department.

Homeland Security spokesperson David Lapan confirmed to CNN that the President's revised executive order "would not affect persons who arrive at our ports of entry with legitimate travel documents."

"The professional men and women of DHS expect 'business as usual' at our ports of entry upon implementation of the March 6 EO," he added.

Why is this happening?

The intent behind the executive order was hotly debated for the past several months.

On the campaign trail, then-candidate Donald Trump called for a "total and complete shutdown of Muslims" entering the US.

But the text of the executive order states that "additional scrutiny" is required for foreign nationals traveling from the six identified nations because "the conditions in these countries present heightened threats. Each of these countries is a state sponsor of terrorism, has been significantly compromised by terrorist organizations, or contains active conflict zones."