US President Joe Biden has instituted a broad asylum ban on migrants caught illegally crossing the US-Mexico border – a major enforcement move in the run-up to November elections that will decide control of the White House.

Migrants caught crossing illegally could be quickly deported or turned back to Mexico under the measure, which will take effect immediately. There will be exceptions for unaccompanied children, people who face serious medical or safety threats and victims of trafficking, the US Department of Homeland Security said.

"We must face the simple truth – to protect America as a land that welcomes immigrants, we must first secure the border and secure it now," Biden said.

"The simple truth is, there is a worldwide migrant crisis. And if the United States doesn't secure our border, there's no limit to the number of people may try to come here because there's no better place on the planet than the United States of America."

Biden rolls out migration order that aims to shut down asylum. – AP

Biden, a Democrat, has toughened his approach to border security as immigration has emerged as a top issue for Americans in the run-up to November 5 elections where he will face Republican Donald Trump.

Biden took office in 2021 vowing to reverse some of Trump's restrictive immigration policies but grappled with record levels of migrants caught crossing illegally, a trend that has strained US border authorities and cities receiving new arrivals.

"The new deterrent measures will significantly increase consequences for those who cross the southern border unlawfully," the official said.

The new asylum restrictions are not permanent, the US official told reporters. They are activated when the daily average of border arrests tops 2500 over a week and will be paused when arrests drop below 1500 per day, the official said.

The last time crossings fell to that level was in the early months of the Covid-19 pandemic in July 2020 when global travel was at historic lows. US border arrests averaged 4300 per day in April, according to the most recent government statistics available.

AP EXPLAINS: Biden rolls out migration order. – AP

Key operational questions about how the new measures will be implemented remained unclear, however, including how the administration would quickly deport migrants from far-away and uncooperative countries and how many non-Mexican migrants Mexico would accept under the new enforcement regime.

The new restrictions resemble similar policies implemented by Trump and use a legal statute known as 212(f) that served as the underpinning for Trump's travel bans blocking people from several majority-Muslim nations and other countries.

The new restrictions are expected to trigger legal challenges from immigrant and civil rights groups who have criticized Biden for adopting Trump-like policies and backtracking on US legal obligations to asylum seekers.

"We intend to sue," said Lee Gelernt, an attorney for the American Civil Liberties Union who helped block Trump-era asylum restrictions.

"A ban on asylum is illegal just as it was when Trump unsuccessfully tried it."

When it comes to immigration policy, registered voters prefer Trump over Biden by a 17 percentage point margin, according to a Reuters/Ipsos poll conducted in mid-May.

The measures were attacked from both sides of the political spectrum.

Migrants reach through a border wall for clothing handed out by volunteers in San Diego. – AP

Republicans criticized Biden's new restrictions as politically motivated and insufficient, while some Democrats slammed Biden for undercutting access to asylum and embracing a Trump-like approach.

"President Biden has undermined American values and abandoned our nation's obligations to provide people fleeing persecution, violence, and authoritarianism with an opportunity to seek refuge in the US," said Senator Alex Padilla, a Democrat from California.

Inaction in Congress 

Biden has pushed unsuccessfully for months to pass a Senate bill that would toughen border security, including with a provision that resembles his latest moves by executive action. The bill was crafted by a bipartisan group of senators but Republicans rejected it after Trump came out in opposition.

"Legislation is still the only way to permanently address border security and immigration reform," White House deputy press secretary Andrew Bates said.

The number of migrants caught crossing the US-Mexico border illegally dropped in recent months, a trend US officials partly attribute to increased Mexican enforcement.

Claudia Sheinbaum was elected as Mexico's first female president in a landslide victory on Sunday and will take office on October 1. Biden's border restrictions could put pressure on Sheinbaum, the successor to current President Andres Manuel Lopez Obrador, to keep illegal border crossings down.

A woman carries her child after she and other migrants crossed the Rio Grande and entered the US from Mexico. – AP

Lopez Obrador said at a daily press conference that he expected to speak with Biden over the phone as soon as Tuesday and that the countries "have been making good progress" on the issue of immigration.

Under the new measures, migrants who demonstrate a fear of being returned to their home countries will be screened for other types of humanitarian protection but could be deported if denied, the Biden official told reporters. Those who are removed will face at least a five-year bar to reentry and potential criminal prosecution.

"These steps will strengthen the asylum system, preventing it from being overwhelmed and backed up by those who do not have legitimate claims," the US official said.

However, Enrique Lucero, the director of migrant affairs in Tijuana, Mexico – across from San Diego, California – warned the new measures could overwhelm migrant shelters as more people will be stuck waiting or returned.

The Biden administration has taken a number of steps over the past year to toughen the asylum process, including issuing a regulation in May 2023 that heightened the standard for an initial asylum claim.

Biden officials have said the effectiveness of US enforcement is limited by a lack of resources in the absence of more funding from Congress.

How Biden's new order is supposed to work

President Joe Biden on Tuesday unveiled a halt to asylum processing at the US border with Mexico when illegal entries reach a threshold that he deems excessive.

The measure takes effect immediately because the new policy is triggered when arrests for illegal entry reach 2500. About 4000 people already are entering the US each day. It was a major policy shift on a critical election-year issue that’s exposed Biden to Republican criticism over an unprecedented surge in new arrivals in an election year.

The measure

Advocates say it will put migrants in danger and violate international obligations to provide safe haven to people whose lives are threatened. The Biden administration denies that.

Legal challenges are imminent.

There are also serious questions of whether the new measure can stop large-scale migrant entries. Mexico has agreed to take back migrants who are not Mexican, but only in limited numbers. And the Biden administration doesn’t have the money and diplomatic support it needs to deport migrants long distances, to China and countries in Africa, for example.

Those who claim asylum today are generally free to live and work in the United States while their claims slowly wind through overwhelmed immigration courts.

How will this play out the ground?

The threshold triggers a halt on asylum until average daily arrests for illegal crossings fall below 1500 for a week straight. The last time crossings were that low was in July 2020, during the depths of the Covid-19 pandemic.

The pandemic-related asylum restrictions known as Title 42 carried no legal consequences and encouraged repeat attempts. Now, migrants will be issued deportation orders even if they are denied a chance to seek asylum. That will expose them to criminal prosecution if they try again and ban them for several years from legally entering the country. It’s a key difference.

“We are ready to repatriate a record number of people in the coming days,” Blas Nuñez-Neto, assistant homeland security secretary for border and immigration policy, said in a conference call for Spanish-language reporters.

Migrants who express fear for their safety if they’re deported will be screened by US asylum officers but under a higher standard than what’s currently in place. If they pass, they can remain to pursue other forms of humanitarian protection, including those laid out in the UN Convention Against Torture.

Unaccompanied children are exempt, raising the possibility that some parents may send their sons and daughters across the border without them.

What role does Mexico play?

A critical one.

The US has limited funding to fly people home to more than 100 countries, including many in Africa and Asia. It also lacks diplomatic sway and logistical arrangements to deport large numbers to many countries, including China, Russia and Venezuela.

A 1997 court order generally limits detention of families with a child under 18 to 20 days, a highly ambitious and perhaps unrealistic turnaround time to screen people who express fear of deportation and then put them on a flight.

Even for single adults, US Immigration and Customs Enforcement has enough funds to only detain about 34,000 people at a time.

Mexico has agreed to take back up to 30,000 people a month from Cuba, Haiti, Nicaragua and Venezuela, in addition to Mexicans. Its commitment does not extend to other nationalities.

This year, Mexico has also made it far more difficult for migrants to reach the US border, largely by preventing them from riding freight trains and stopping them on buses to turn them around to southern Mexico. While Mexican authorities are blocking migrants’ advance, relatively few are deported, causing many to be stuck in Mexican cities far from the US border.

Alicia Bárcena, Mexico’s foreign relations secretary, told reporters last month that Mexico won’t allow more than 4000 illegal entries a day. President-elect Claudia Sheinbaum, who takes office October 1, is expected to continue policies of her mentor and Mexico’s current president, Andrés Manuel López Obrador.

Has this been tried before?

This is the latest in a series of measures under the Biden and Trump administrations to deter asylum-seekers, none of which have had lasting impact.

In May 2023, Biden imposed similar obstacles to asylum for anyone who crossed the border illegally after passing through another country, such as Mexico. A federal appeals court allowed those restrictions to stay in place while advocates challenge it, but it appears to have little impact.

Illegal crossings fell after last year’s restrictions took effect, but the lull was short-lived as the number of screening officers was inadequate for the enormous task. The rule’s application in only a small percentage of arrests showed how budgets can fail to match ambitions.

Biden invoked a section of the Immigration and Nationality Act that allows the president to ban entry for groups of people if their presence “would be detrimental to the interests of the United States”. Former president Donald Trump used these powers to ban entry of people from some predominantly Muslim countries, though advocacy groups are expected to argue that Biden failed to meet that “detrimental” criterion.