President Trump’s abrupt announcement Monday night that he will temporarily suspend all immigration into the U.S. amid the coronavirus pandemic raised more questions than it answered.

White House officials have provided little information beyond the president’s tweet, which offered no details on when the suspension would take effect, how it would be enforced or how long it would last.

Experts say the executive order, which was still being finalized as of Tuesday, is unlikely to have a major impact given most paths to immigration have already been halted due to the pandemic. But the timing has given fodder to critics who believe Trump is seeking a distraction from his administration’s handling of the coronavirus.

The president’s allies have defended the announcement as an effort to prioritize American workers at a time when unemployment is hitting historic highs. However, the final order may offer exemptions for farm laborers, medical workers or others with visas who can fill jobs many Americans are unwilling or unable to perform.

Administration officials on Tuesday struggled to offer clarity on the executive order.

National security adviser Robert O’Brien said the measure was “not dissimilar” to the administration’s January ban on non-citizens traveling to the U.S. from China, though that policy targeted the center of the virus outbreak before there was known widespread transmission.

While the new restrictions on travel from Canada, Mexico and Europe are subject to review every 30 days, O’Brien did not offer a time frame for suspending immigration.

“We’ve flattened the curve, we’ve been able to avoid the health systems being overrun, and so that’s all good. But we’ve still got a long way to go on this,” O’Brien told reporters at the White House. “We need to bring the economy back, and so we’ll monitor all of those factors as we make decisions on travel restrictions and immigration restrictions.”

White House press secretary Kayleigh McEnany argued in a statement that the president’s action will protect American workers from overseas competition at a time of increasing unemployment. But she did not offer any specifics on the policy.

The Department of Homeland Security (DHS) did not respond to questions about the order or how it might affect visa programs. The agency last month announced the availability of 35,000 supplemental H-2B visas for non-agricultural workers. It remains unclear how Trump’s order would impact visas for workers or their family members.

A draft version of the executive order included a provision for some H-1B visa holders — the most common temporary work visa — to update their labor certifications to prove they’re not displacing American workers, according to Bloomberg News.

It’s unclear to what degree the order would alter U.S. policy changes previously implemented during the pandemic. One State Department source suggested the new order is unlikely to affect visa operations more than they already have been.

The Trump administration in late March temporarily suspended all routine visa services at U.S. embassies and consulates, meaning most foreigners cannot apply for a visa.

The State Department said at the time it would continue to provide emergency and mission-critical visa services “as resources allow.” The administration has allowed medical professionals to come work in the U.S. but only if they have received an approved visa petition or qualified for an exchange visitor program.

Many immigration experts view Trump’s late-night tweet as bluster and nothing more than a PR stunt.

“The consulates are already closed. They’re not providing interviews except for special cases,” said Ur Jaddou, the director of DHS Watch, an oversight program at the progressive advocacy group America’s Voice.

“The practical effect of this is that [immigration] is already closed down,” added Jaddou, former chief counsel at United States Citizenship and Immigration Services, the agency that grants work permits and naturalizations.

Alex Nowrasteh, the director of immigration studies at the conservative Cato Institute, said the short-term consequences of an executive order would be negligible.

“The only realistic justification is a political move. He’s trying to shore up his nativist supporters and trying to show them he still cares about the topic,” Nowrasteh said.

But he warned that in the mid to long term, a reduction in skilled immigrant labor could paralyze industries that depend on foreign workers.

“If it carries on past the emergency, past any reasonable safety period of time, there could be very serious economic ramifications,” said Nowrasteh.

Officials have also expelled thousands of migrants arriving at the U.S. border after the U.S. and Mexico agreed to travel restrictions, which were extended Monday.

Those expulsions have been conducted under the auspices of protecting public health, which leaves open the possibility that a new executive order could go beyond the known limits of immigration law.

“I am shocked they used public health law to do the things they’re doing at the border, what they’re calling expulsions,” said Jaddou, adding that she wondered whether the administration has found a statute outside immigration laws to enforce a new policy.

“I’d be surprised, but you never know with this administration,” she said.

Meanwhile, there are doubts among public health experts as to whether such a suspension would alter the trajectory of the pandemic domestically. There are roughly 789,000 cases of COVID-19 in the United States, according to data collected by Johns Hopkins University.

“I think what it does is it conflates public health policy with immigration policy and I think they have very different purposes and political symbolism,” said Lawrence Gostin, a professor of global health law at Georgetown University.

“It seems to me that we’ve already got widespread community transmission in the United States and this would not change the trajectory of the epidemic here at all,” he added.

The president has made curbing legal and illegal immigration a cornerstone of his presidency. He has imposed travel bans on certain countries, rolled out executive orders making it more difficult to apply for asylum and floated an executive order to end birthright citizenship.

But the prospect of halting immigration entirely as the world attempts to coordinate on combating the coronavirus marked an extraordinary extension of his push to tighten U.S. borders.

The new order, whatever form it takes, will likely face an immediate legal challenge.

“The Supreme Court has given the president a very wide berth on questions of immigration,” said Gostin. “I think it will be challenged, but it will be hard to succeed.”

Still, foreign nationals already in the United States are likely to contest any measures that narrow the scope or duration of their existing permits.

“If they’re inside the United States, they’re protected by the laws and they can sue,” said Jaddou.

Trump’s previous attempts to curtail immigration or travel into the U.S. have been marked by discord.

His first attempt at imposing a travel ban shortly after taking office triggered chaos and protests at U.S. airports as travelers were detained upon arrival. The ban was later struck down by the courts until a watered down version was upheld by the Supreme Court.

The president misspoke during an announcement last month restricting travel from most of Europe, setting off a brief panic about the closure of commerce before he corrected the matter on Twitter. The White House did not provide advance notice to European diplomats, and Americans abroad scrambled to catch flights home, which overwhelmed domestic airports. Trump also was forced to extend the ban to the United Kingdom and Ireland days later after pushback over their initial exclusion.

Laura Kelly contributed reporting.