It’s here. President Trump’s travel ban — after two executive orders, several court rulings, and a huge administration victory from the Supreme Court — is back.

At 8pm Eastern time on Thursday, the ban — which temporarily bars some people from getting visas if they come from Iran, Libya, Somalia, Sudan, Syria, or Yemen for the next 90 days, as well as barring an untold number of refugees for 120 days —went into effect in airports around America and consular offices around the world.

The administration appears to be trying to avoid the chaos that plagued the first iteration of the “travel ban,” which was in effect for a week after getting signed in late January but was ultimately put on hold by the courts. (The version going into effect tonight was a modified executive order signed by President Trump in March, and further modified by a Supreme Court ruling on Monday that allowed the ban to partially go into effect while the courts weigh its constitutionality.)

This time, the administration’s trying to set clear rules about who will be allowed to enter (thanks to the Supreme Court’s mandate to the Trump administration on Monday) because they have a “bona fide relationship” with someone or something in the US.

But they’re already hitting snags.

Mere minutes before the ban was set to go live, the State Department reversed itself to allow fiances of people in the United States to enter the country.

Advocacy groups are still upset by the administration’s narrow definition of “bona fide” family relationships (which still excludes grandparents). And the government is hinting that refugees who’ve been placed with a resettlement agency won’t be allowed to come to the US unless they have close family members here — which would severely limit refugee resettlement in the US over the next 4 months.

And it’s still impossible to rule out the possibility that something will go down in the airports.

Here’s what we know — and what we don’t.

What we know

Starting at 8 pm Eastern on Thursday, US consulates and embassies around the world will no longer approve visas for people traveling on passports from Iran, Libya, Somalia, Sudan, Syria, or Yemen to come to the United States, unless those people can establish a “bona fide relationship” with someone or something in the US.

A “bona fide relationship” can be with a business or university in the US — for example, if the person has a job offer or a conference invitation — or it can be with certain family members.

Only certain family members, however, will count as “bona fide” relationships. According to the State Department cable, applicants (or refugees seeking to be admitted to the US) who have a “parent (including parent-in-law), spouse, child, adult son or daughter, son-in-law, daughter-in-law, sibling” or half sibling — or a “step” version of any of those relationships (stepparent, stepchild, etc) — in the US will be approved, because that relationship counts as “bona fide.” But other relationships don’t — including grandparents and grandchildren, aunts, uncles, nieces, nephews, and cousins.

Initially, fiancé(e)s of people living in the US were not considered “bona fide” family. But 15 minutes before the ban was supposed to go into effect Thursday, the State Department updated its FAQ to state that fiancé(e)s were supposed to be granted visas.

People traveling for business, meanwhile, are only going to get visas if the US government determines that they’re not just being invited to the US to circumvent the ban.

There are exceptions. Consular officers are supposed to grant visas to people who’d otherwise be banned in some particular circumstances — for example, if they’re in need of urgent medical care or doing business with the US government — or if the officer (with leadership approval) decides that denying the visa would cause undue hardship and allowing the person to come is in the US’ national interest.

Anyone who already has a valid visa as of 8 pm Eastern on Thursday is supposed to be allowed into the US, according to President Trump’s executive order.

What we don’t know

What the ban means for refugees who don’t have “bona fide” family members in the US according to the categories laid out by the State Department. Many advocates have argued that the Supreme Court’s ruling should permit nearly all refugees to enter the US, because refugees have to be placed with a resettlement agency before entering the country, and that should count as a “bona fide” relationship. But the Supreme Court didn’t specify that, and the administration doesn’t seem to be taking it that way.

In a press call on Thursday, a senior administration official said that “the fact that a resettlement agency in the United States has provided a formal assurance for refugees seeking admission is not sufficient, in and of itself, to establish a bona fide relationship under the ruling.” It’s not yet clear whether this means refugees will only be admitted if they already have close family in the US, or whether some stage in the resettlement process will count as a “bona fide” relationship. And all refugees who are scheduled to arrive in the US through July 6th will be able to come without incident. But after that, tens of thousands of refugees, and the resettlement agencies in the US that employ people to help them, remain under a cloud of uncertainty — and it’s not looking good.

Whether Customs and Border Protection agents will cite the ban to detain anyone entering the US. Senior administration officials assured the press on Thursday that people with valid visas would be allowed into the US once the ban went into effect Thursday night. And because no one’s allowed to board a US-bound plane without a valid visa, there shouldn’t be any problems for anyone landing in the US. However, the overly-aggressive and inconsistent implementation of the first version of this executive order, back in January, has made many lawyers and advocates worry that CBP agents might be overly aggressive, or poorly trained, in implementing this guidance. Pro bono lawyers are already stationed at many international airports around the US, hoping to monitor how people coming in are being treated.

How generous consular officers are going to be in granting waivers for “undue hardship.”

How transparent consular officers will be in denying visas — and CBP officers will be in denying admission to people arriving in the US. The US government can deny a visa for almost any reason, and it’s near-impossible to challenge a visa denial. People who are from the 6 affected countries but have a “bona fide relationship” could still be denied visas for other reasons. And even if someone has a valid visa and comes to the US, the government (through CBP) has wide latitude to stop him from formally entering.If such denials are common, it might raise the suspicion that the government is using other criteria for visa denial and admissibility as a backdoor way to expand the scope of the ban.

Whether US courts are going to agree with the Trump administration’s interpretation of “bona fide” family members. US immigration law has always made distinctions among different types of family relationships. But the Supreme Court’s ruling didn’t make any distinctions among degrees of relationship when it set the standard for a “bona fide” relationship on Monday, and it’s not clear whether the courts will agree that it’s fair to say a grandmother doesn’t have a “bona fide” relationship with her grandchild. It is a near-certainty that, as soon as visas start getting denied under the ban, the US-based relatives will claim the Trump administration has violated the terms of the Supreme Court’s order by implementing the ban even when it wasn’t supposed to, and there will probably be a profusion of lawsuits. The question is whether federal courts will side with families or with the government, and whether — with the Supreme Court out for the summer — various courts around the country will come to different conclusions and create a patchwork of interpretations of the ban.

UPDATE: This article has been updated to include details from the full text of the State Department cable, and from reports of a press call with senior administration officials.