President Biden on Tuesday unveiled new executive action authorizing U.S. immigration officials to deport large numbers of migrants without processing their asylum claims, announcing what is arguably the most restrictive border policy by a Democratic president in recent history.

Mr. Biden's aggressive move suspends the processing of asylum claims between official entry points along the southern border, allowing U.S. authorities to more quickly reject and deport migrants who enter the country unlawfully.

"If an individual chooses not to use our legal pathways, if they choose to come without permission and against the law, they'll be restricted from receiving asylum and staying in the United States," the president said in remarks at the White House.

The partial ban on asylum claims will take effect at 12:01 a.m. Wednesday. Regular asylum processing will only be restored 14 days after the secretary of homeland security determines that the weekly average of daily illegal border crossings has dipped below 1,500. The proclamation could be activated again if the weekly average of daily crossings between ports of entry surpasses 2,500.

To the dismay of migrant advocates, the seismic policy change attempts to upend U.S. asylum law, which allows migrants on American soil to request humanitarian protection, even if they cross the border illegally. But Biden administration officials have argued the asylum system is buckling under the weight of over 3 million pending applications, incentivizing migrants to come to the U.S. because it takes years to decide their cases.

What Biden's immigration order does

Mr. Biden made the policy changes through a presidential proclamation that temporarily suspends the entry of most migrants at the southern border. The Departments of Justice and Homeland Security published a regulation to implement his directive. 

"I must exercise my executive authorities to meet the moment," Mr. Biden's order said. "This proclamation answers the call by suspending entry of noncitizens across the southern border during this time of high border crossings."

Migrants who cross the U.S.-Mexico border between legal entry points when the order is in effect will be barred from asylum and "immediately removable" to Mexico or their home countries, officials who previewed the move said. The administration, one official added, plans to carry out these deportations "in a matter of days, if not hours."

Only migrants who affirmatively express fear of being persecuted or tortured will be screened by U.S. asylum officers, the officials said. But they will only be screened for lesser-forms of protection — not asylum — and will need to pass interviews with heightened standards to avoid being quickly deported.

The asylum crackdown will not apply to unaccompanied children, those with acute medical conditions or fleeing imminent harm and migrants who use legal pathways to enter the U.S., such as the system powered by the government smart phone app known as CBP One. The administration will continue to process roughly 1,500 migrants at ports of entry under the CBP One process.

To justify the policy shift, the administration is citing a 1950s law known as 212(f) that empowers the president to suspend the entry of foreigners when the executive branch determines that their arrival is "detrimental" to U.S. interests. That same law became infamous under the Trump administration, which invoked it to sharply restrict legal and illegal immigration, including travel from certain Muslim-majority countries.

The American Civil Liberties Union said it will challenge Mr. Biden's actions in court. "We intend to sue. A ban on asylum is illegal just as it was when Trump unsuccessfully tried it," Lee Gelernt, a top ACLU attorney, told CBS News.

Officials said the partial asylum ban applies to so-called extra-continental migrants, such as those from China, who have been journeying to the U.S. border in record numbers in recent years. But they did not say Mexico had agreed to take them back, raising the specter that some migrants will still be released with court notices since certain countries, including China, limit or reject U.S. deportations.

A major policy and political shift

Mr. Biden's policy is modeled after one of the pillars of a bipartisan border security deal that failed twice in Congress due to widespread Republican opposition, giving administration officials an opportunity to argue they are acting unilaterally on one of Americans' top concerns in the absence of congressional action.

The proclamation lays the blame for the problem squarely at the feet of lawmakers.

"The current situation is also the direct result of the Congress's failure to update an immigration and asylum system that is simply broken — and not equipped to meet current needs," it said. "While my Administration has vigorously enforced the law within the constraints imposed by the existing system, the statutory framework put in place by the Congress is outdated."

In his remarks, the president said he was "moving past Republican obstruction and using the executive authorities available to me as president to do what I can on my own to address the border."

"Frankly, I would have preferred to address this issue through bipartisan legislation, because that's the only way to get the kind of system we have now, that's broken, fixed," he added.

While sweeping in nature, the announcement does not completely "close" or "shut down" the southern border, as asylum processing and legal trade and travel will continue unimpeded at official ports of entry. 

In many ways, Mr. Biden's drastic border pivot stems from the intense political pressure he has faced from Republicans and some Democrats on immigration, one of his worst-polling issues. 

But it is also in response to the reality on the ground along the U.S.-Mexico border, where American officials have reported record levels of migrant apprehensions, including over 2 million in each of the past two years. This year, migrant apprehensions are down by more than 50% from the all-time highs recorded late last year, partially due to a months-long campaign by Mexico to stop migrants from reaching the U.S. border.

Andrea Flores, a former Biden administration official, denounced the president's move, saying it could set a dangerous precedent.

"If the president is now claiming he can shut down asylum when he feels like it — even after border numbers have plunged by over 50% — this precedent gives future presidents the pretext to suspend any immigration pathway to the United States," said Flores, now the vice president of immigration policy at FWD.us, a progressive advocacy group.

GOP lawmakers also largely dismissed the move as an election-year maneuver that would do little to change the realities on the ground.

"President Biden's Executive Order is nothing more than a desperate political stunt to try and stabilize his plummeting poll numbers," House Republican leaders said in a statement. 

Sara Cook contributed reporting.

Camilo Montoya-Galvez

Camilo Montoya-Galvez is the immigration reporter at CBS News. Based in Washington, he covers immigration policy and politics.

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